This thread is a massively heartening to me, just knowing so many of us are in the same boat.
I was a fairly cosseted child- never had to do much housework, mend my clothes, MOT my car...my mummy and daddy did most of that and I only had to make token efforts to help. So all of that stuff.
How much houses cost. We lived in a nice big (inherited) house, the cleaner came once a week, enough money for expensive hobbies etc. I assumed that as I was academically clever and got into a sought-after degree course with a professional job at the end of it I'd be able to afford a nice big house like that in my early 30s like my parents were when they got the house. In fact in my early teens, I didn't think I'd need to get a mortgage when I grew up: I planned to get a job and work hard and live fairly frugally and then I'd have saved enough money to buy a nice big house outright 
I am nearly 40 and now count myself lucky to be able to afford, with combined input from husband+my FT jobs, a small house with tiny rooms and 20ft of garden, which it will take me years to pay off. Shit virtually non existent pensions so we will also probably work till we drop. And we have it financially easier than quite a lot of people we know.
Parental illness: I was fully prepared for my smoker dad to get lung cancer. Such a big deal made of it in school etc that I thought it was a cert and on occasion cried myself to sleep worrying that my lovely daddy might already have it.
I needn't have worried.
He didn't get lung cancer.
He got dementia.
Things life doesn't prepare you for: knowing what dementia is like. It's not some kindly really elderly people going benignly but pleasantly dotty.
Going by dad and the other patients in his various nursing homes, most people with dementia- many of whom are younger than you'd think- spend a lot of their time scared, bored, in pain, angry, self pitying, unable to do or even take much or any interest in 99% of the things they used to and there is only so long you can make the 1% last each day; and the physical decline is rapid and savage. But they can stay living and suffering for a long time.
Trying to make their life a bit less shit for the length of your weekend visits then getting in the car and driving up the road on Sunday night to get stuff ready for self and child to leave the house for 7.30am nursery dropoff and into work to start again.
Looking at your lovely nice kind daddy who used to buy you sweeties lying in a coffin. Well of course everyone expects their parents to die before them but....the feeling right in the moment when you're walking out of the room knowing the lid is about to go on and you will never ever ever see them again.....