To tell son it’s too much and affecting his dad’s self esteem.

Criticises you for having a lie-in? Was he always up at the crack of dawn when he was a teenager?

Criticises you for the food you eat? Did he live on broccoli and tofu when he was a teenager?

Did he always listen to your advice when he was a teenager?

Thought not. Hypocritical. Tell him that he lives his life and you live yours and he can butt out.

He sounds worried about his dad. It's not surprising when you have the attitude that 55 is too old to change an unhealthy lifestyle. At 25, he'll be becoming aware of you and his dad's mortality. Watching his dad eat and slob his way into an early grave probably gives him a lot of anxiety.

Maybe your DS is worried about his father’s health and is trying to suggest how he should live to have him live longer but is going round it the wrong way.
You say yourself that DP is a couch potato, could you suggest some simple changes by going out for strolls/walks weekends and try to change bad food habits.

I did, my late DM would have thought it odd if I didn’t. I would never have gone round there at such an ungodly hour though, unless it was an emergency of some kind.

Be direct. Say DS, that's enough, you're being really rude and judgemental and if you can't stop yourself, we don't want you coming round here. Your nasty attitude is not welcome. I don't care if you think you're right. If you can't show some manners, you need to leave. You're not too old for a bloody slap.

Have you tried embarrassing your son into shutting up? I would ask him to stop interrupting your bedroom activities with his early morning visits. I am sure he will be horrified! Especially if you add 'its the most exercise your dad gets'.nudge, nudge, wink wink.

Tell DS that unsolicited, negative opinions and instructions are unacceptable and undermine connection in relationships.

It’d be better for him to ask for one proper talk with his dad about his (understandable) concerns about his health risks. It’s entirely up to DH what he does or doesn’t do and DS should refrain from criticising, having been explicit about his concerns and opinions.

Similarly if DH is part of a competitive dynamic with DS over difficult things he could reflect on that.

presumably you all wants to transition adult to adult relationships, with mutual respect etc, and DS (and DH if they ‘spar’)wouldn’t treat other adults like it.

Even with a key to the house, I would never have just let myself into my parents home once I wasn't living there. It's bloody rude I think.

Your son needs some advice back. He sounds, I am afraid as if he has no or very little emotional intelligence. And a distinct lack of respect for you both.
Some feedback perhaps is overdue.

He doesn't sound "lovely"

He sound like a rude sanctimonious prick

Small point, and not the main point I realise, but I'd just add a bolt to the door.
Would cause less aggro than changing the lock and you just leave the bolt closed until you're happy for DS to come in (as long as you are happy - I wouldn't expect my DC to just let themselves in and I wouldn't do it to them either).

Barely an adult ? He is a 25 year old man and needs to learn some manners.

Is DH a bit chubby, or are we talking medically obese etc. I say that as a 54 year old (Male) who's put on a stone in the last year.

He's probably worried about his dad shuffling off early?

Be honest, are you as well..?

Rather than trying to turn (us) 50 year olds into gym rats, would your son be able to come round and go for walks etc with DH?

If I'm honest, I worry about getting diabetes etc - so I'm not coming from some super smug angle. I've already had a millionaire shortbread in a coffee shop this morning.

Mind you, my lovely DD is safely away at uni - so I've no idea what she thinks of us old farts!

So many replies suggesting it’s concern, and maybe DH should do something about his weight. No. Tell him directly, as a couple, one last time that this needs to stop as DH is an adult and doesn’t need his son telling him how to live his life, if he continues I’d tell him he’s being insufferable and no one likes a nag, and ask he not visit for a few weeks to have time to reflect on his nasty behaviour, because continuing to say those things after being asked to stop, is nasty

Well, your DS is being insufferable and sanctimonious, which I can see is extremely annoying, but your DH sounds like he's heading for an early grave tbh. Being obese and inactive and eating crap in midlife is a recipe for a heart attack and yes, it is his life to live as he wishes, but a lot of people (my DH included) turn things around in their 50s, so it's not impossible. Why doesn't your DH care about his health? Doesn't he care that, at the very least, he's like to end up with mobility problems as he gets older and quite possibly Type II diabetes and all the health complications that that entails.

Sympathies, OP; one of ours still lives with us and lectures dh a lot.

Thing is, mine has a point. DH doesn't follow dietary guidelines for his health conditions (he thinks he does, while absent mindedly hoovering up crisps and pastries "just this once") or the exercise guidelines (again, he thinks he does, but it's not nearly enough). Does your DH have anything medical going on?

So take the key back and tell him not to come round without prior arrangement. It's your house. He does not have proprietary rights over it just because he used to live there.

Young people can lack self awareness. It's very easy when you are a young adult to think you know everything. I'm sure I was insufferable more than once.
I'd tell Judgemental Judy to stop being so unkind and so rude and to spend some time off his bike learning some emotional awareness. But then I'm quite open with my son. Alternatively I like the idea up thread of telling him you're in bed as you're having sex.

I’d certainly be either taking his key away or changing the locks! What sort of person turns up so early, unless just to be critical?

Plus I’d be telling him that we don’t answer the door before 9 am, and 10 at weekends.

Yes this. OP change the locks and tell him he’s not getting a key until he stops giving you and your DH grief about your lifestyle.

time to get the key back off him, he doesn’t need it.

My Dad has always got pissed off when we’re on at him to be healthier, and he’s actually quite active. So we dont say anything very often. However, the lifestyle he got away with at 55 is not sustainable and in early 70s there started a string of health issues some of which would have been less serious or non-existent if he took better care of himself. I don’t want my Dad to die. Your son is young and has not yet learned to be diplomatic, but he might have a point (except for the lie-ins bit).

It doesn’t really matter if your son is coming from a place of concern, his approach is creating entrenched positions on either side that are likely to mean your H is less likely to improve his health and is also damaging all your relationships.

You son has no idea of how to win friends and influence people. If he behaves like this in other relationships, he’s going to damage those too.

I would explain this to your son and also be clear that his approach means this subject is now banned and he will be told to leave everytime he brings it up. When the dust has settled a bit I would gently raise starting a different lifestyle with your H. as he is facing premature disability and ill health. My poor FIL also eschewed ‘exercise’ and liked his food. He now needs someone to haul him out of a chair if he wants to get up and if he falls at home, he has to just lie there till someones comes home to help him up. Thats no way to live.

He doesn't sound lovely he sounds bored, sanctimonious and maybe unhappy with his lot so turning on you, I would take his key off him or certainly tell him he isn't welcome at 9 am and to stay out of your fridge, you have probably indulged him too long he is an adult child he needs to start respecting your boundaries you have to tell him.

Tell him to stop coming round so early too. You and his Dad skirting around the issue isnt going to teach this little turd that hes seriously overstepping. His behaviour is awful and I dread to think how hes going to act in any relationships.