Does everyone turn “funny” or bitter in the old age?

No, of course they don't all. My maternal grandparents were lovely until the end. Never knew my paternal grandfather. Grandmother had dementia for quite a long time.
Dh's and my parents are late 70s-early 80s. The only one who at all fits your labels is my mum, but with good reason. She has earlyish dementia, is very immobile and her life is just one long round of medical appointments. She's had enough.

at the very end, a lot mellow out and become childlike.
i think a lot made choices and suffered and want the next generation to make the same choices to make that suffering worth it

My dad and FIL are the same age (75), both widowed. They couldn't be more different

FIL has social hobbies and exercises , travels globally, still has football season ticket. Very engaged with his grandchildren Retains a really positive outlook despite his knocks in life. He's inspiring.

My dad is slowly drinking himself to death, is depressed but won't seek help. Barely leaves the town he lives in, plans nothing if we visit. Definitely sees himself as a victim and can be bitter but he was always this way.

My 8 year old describes one of her grandads as "old" but not the other. I know who I hope to be...

I think it's very easy to become socially isolated and less open-minded with age. I see this with three of my elderly relatives, but particularly aunt and MIL, neither of whom make any effort socially any more. Both are in their 80s, both able-bodied, but have become very reclusive and resentful of those who aren't. How to avoid becoming like this and also bitter, which tends to accompany this behaviour? Don't become a recluse!

My DF is still fully engaged with life. He meets friends, volunteers, drives, visits people, has people over, walks his dogs, gardens, travels, reads widely, listens to music and the news. He's as engaged with life as I am and he's always in and out. Yes, he's had some health problems, he has some pain and stiffness, but he gets up every day and gets on with his life. Age is not preventing him from living a full and interesting life. He's an example to me. My DGM was the same - always doing things, seeing people, getting out and about. That's how I plan to be until I am no longer able or I drop dead.

My Mother was a bitter twisted narcissist.

She didn’t get better with age, she just forgot who she told what lies to so got more frustrated.

She ended up in a home with dementia, one of the staff told me once how she understood my infrequent visits as she had witnessed her vitriol.

I really think it’s personality and you are unpleasant or pleasant.

Old person and medical secretary (still working albeit very part-time) here.
In my experience, many older people suffer from depression, hence the gloomy, grumpy behaviour. A small dose of antidepressant can make a huge difference. They are often prejudiced against taking antdepressants. My mother wasn't keen but I asked the GP (who had asked me if she might be depressed) to be the one who asked her to try medication as I knew she wouldn't listen to me. It made a huge difference to her mood and she started taking an interest again. Some of my aging contemporaries are starting to get low in mood too. I think it is deteriorating health in general, loneliness (living alone after a lifetime of having children and partner around them and having too much time on your hands (some people have never had any hobbies or like reading, etc).

Absolutely, I agree with this too.

I had a lot of horrible health problems over the past decade, including a head injury and post concussion syndrome before being injured permanently by an off label antipsychotic that gave me a neurological involuntary movement disorder called tardive dyskinesia.

I've made a huge effort to try and be as positive as possible, even during very frightening times with my movement disorder and having an adverse reaction to medication etc. It's helped having three children to focus on too, as they really are the thing that keeps me going.

I also read a good article this morning that said about how constant negativity can absolutely reshape your brain, reducing the hippocampus and memory. However, it's also possible to rewire and change it through being positive. Neuroplasticity is certainly a thing too. Being in nature daily helps hugely too.

The type of person you mom is is hardening due to age, trauma, and life circumstances. Things haven't turned out as she imagined and she's bitter.

I think a turning inwards and introspection happens with aging. If that's positive and you like what you see, that helps with attitude. I think that has to be balanced with remaining engaged in the world outside you too.

My parents were really lucky, they had a few hobbies and they belonged to a really great social club, where my mother still has the opportunity to belong to a book club, wine tasting, my dad did walking football for grannies.
So they keep really busy, this kept them going.

Probably other factors as well, I think they were nice people so not too bitter.
Could also have been luck, although my father did have a hard childhood, was beaten by his father in a cruel way, but was very kind to us.

Some people have really nasty things happen to them and they get bitter, I do believe that.

Perhaps some have genetic factors alzheimers, mine luckily did not or my mother has not .

Yeah so keeping active and social I think really important

Barring medical issues that can cause personality changes it’s usually a case of those who have always a bit difficult just become more so, their world tends to get smaller so the issues become more pronounced.
My parents were difficult and selfish, the older they got the worse it got but it’s who they always were. FIL has always been and still is a delight in his 90s, my DCs great grandparents were both fabulous until the end.

My uncle recently lost his wife to cancer. He was always a half glass empty person but now is quite negative. He recently complained about seeing videos of us “eating and drinking” on social media at a long overdue family celebration. He choose to share this when I had shared with him I was going through a particularly tough time. I felt he was being deliberately mean due to his own unhappiness. I feel sorry for him but have blocked him from seeing my social media going forward. He is getting worse as he gets older.

My mum and dad are 80 and 90 respectively and are not at all bitter or nasty. They have their flaws and their healty problems, but are still kind, grateful for visits and the help we give them, and adore their grandchildren. I think not seeing them face to face would make communication more difficult though, and change the relationship.

My grandmother was very bitter in the last decade but that came from her DH tricking her into marriage, drinking himself to death after 20 years of them living on a shoe string and when she got his last washer packet she discovered he earned twice what he’d told her. Then she started work and did very well but retired to help some family. The family promptly dumped her 4 months later and moved away and she was left at home with very little family, no friends door to the bitterness, and increasing mobility issues. My mum is now going the same way. I will euthanise myself before I end up like that. I will never ever put demands on my kids and demand visits and help that I could get from elsewhere.

in the flip side, my did is a marvel and exactly who I want to age like. He’s 83 this year, still working part time by choice, runs his own boat, does his own diy, is always out and about with friends and visiting etc. working in hobbies and very positive. My mum ( his ex wife) is ten years younger and filled with vitriol. Its crazy.

Difficult, self-obsessed people are highly unlikely to mellow with age.

Ailing health becoming a barrier to engaging with wider life can turn people more inwards. With one relative who had a great, active 70s, her mental connection with the world faded along with her physical ability. The biggest change was in her late 80s when her daily walk to the village, buying her day's groceries and newspaper got too much and she lost that community connection, news and suduko puzzles. This was shortly before lockdowns which then reduced her world to her house, a couple of family members and healthcare as she slipped into health crises mode in her last couple of years. At least prior to that point, she'd managed about 88 years with the essence of her lovely personality. She used to grumble about the "old" people who were younger than her who mentally gave in to old age because they hit a number, then did start aging rapidly.

I hope I can optimise my body and brain's chances of working as happily together for as long as possible, to have a decent quality of life, and a key part of that is connection with other people.

Exactly.

I think age just accentuates character traits that were always there - the filters just come off.

My GM was awful once she passed 75. She was always whinging about something or other, and every time I sorted out the issue she would just move on to something new. My DF has now turned into a carbon copy of his mother (even though he used to say “if I get like that, shoot me!)
DF spends much of his time on the internet diagnosing himself with various illnesses to account for his general lethargy and aches/pains, but when I suggest solutions ignores them and sits watching tv. I’ve given up 🤷🏼‍♀️

My neighbours - in their 80s - are truly horrible, but then they always were, or at least one of them was. Not sure they can use age as an excuse.

100% agree that the key is to stay interested in life and the people around you. Often that means also having an outside interest like art, politics, hobbies, sport, religion. Which one it is doesn't really matter. The most unhappy older people I have met have been those whose main interest throughout life was themselves. As their own bodies and lives becone more limited, their outlook does too.

My dad was great until my mum passed away. He's really unpleasant to be around and I've backed off a lot. He's fine with other people but myself and my sister take the brunt of it. I wonder if my mum kept him in check when she was alive and this was his true self all along?

I think it's about still living a full life. Life changes as we age, you have to embrace it. It's important to still have things that you want to do and sometimes force yourself out of your comfort zone. It's said being involved in your family, or community is important. My single, childfree sister (70) still volunteers and is very active in her church. She also goes on protest marches etc. I'm my DD's childcare and I do local, interest, adult education/cookery/wreath making etc courses. I'm lucky to have no health issues, so I do some shopping and dog walking for neighbours. I still have a social life. My DP's Mum (83) forces herself to go to bingo and to her local social club, she can't dance anymore, but stands and moves her arms. Too many women allow the grumpy old men they live with, drag them down. Luckily, here in the UK, we can get rid.

I'd say optimism, a sense of humour and generosity have a lot to do with it. My dad has these qualities in spades and has not become cantankerous as he's got older; he's not hugely old though (78).

My DFIL is pretty cool too; he is very loving and generous with family and friends, although he and my DH can sometimes go down a rabbit hole of resentment about bailing out people who don't pull their weight in society (they are both very hard workers and very high tax payers as a result).

I think what PP said about it magnifying your inherent personality traits is very true.

Basically, if you’re a shit young person, you’re probably going to be a shit old
person.

Your daughter’s got it wrong. People don’t get like this because they lose interest in themselves. It happens when they lose interest in other people and the world around them.

No. But according to Mumsnet they do.