Late evening eating

You're getting a hard time here OP. I think because you said DSS rather than DS.

People saying things like "if shopping, meal planning and cooking are such a chore" IF? Of course they're a fucking chore. There are three adults in this house, if your DH is making his contribution by being the main wage earner, what excuse has his son got? He's not even covering his own food costs.

You're not his maid, he needs to clean up after himself. He needs to shop for himself for anything he wants outside of the food served as part of a family meal. He needs to stop treating you like Andrew Tate tells him he should

Reheating something in the microwave will be noisier than just making porridge on the hob which creates little to no noise at all.

Likewise eggs. They aren't noisy prep or cooking foods.

I couldn’t live like this… you need a family meeting to sort it out!!! It’s all hands on deck in this house, 13 yrs old DC cooks one night per week for us, DH does meals at the weekends, I do the other four. We have a rota for washing up ware doesn’t make it to the dishwasher - nothing gets left in the sink. And £150 pm is ridiculous rent for a 21 yr old on a good salary WTAF!!!

would it help if he was to buy his own shopping? If he has specific things he wants to eat and he is earning a good wage it seems sensible he buys eggs, bread, etc himself and any snacks he wants

Not a 'house share' per se, but you share a house with other adults and I'm afraid that comes with some compromise. If you want total control over the activities in your house, you have to live alone. You can't dictate the behaviour of other adults whose home it also is, just because you have a preference for something different.

@Blankscreen he must be eating £150 of eggs alone!!! do you have chickens in the garden??? with the legitimate food he is eating more than 150 pounds worth!!

You're annoyed about the wrong things OP. First, DH needs to step up a bit more and stop leaving all the feeding and cleaning to you. (Unless you're a housewife though I suppose). Second, DSS needs to up his rent and help out more. Evening eggs and the odd plate are non issues.
But for that to happen you have to loosen up a bit with your kitchen....

I wonder if OPs own children will have to "respect the schedule/take their turn cooking or move out" when they are older.

Edit to say it doesn't sound like the husband takes a turn cooking. At least OP has said she does it all.

do people really tell other adults living in the house what time they can eat? What if he isnt home at the specified time or isnt hungry?

I have two young adult sons who weight train together several nights a week. I go through eggs and chicken breast like there's no tomorrow. Sometimes I wake up to the smell of chicken being cooked very late at night - it's mildly irritating but it's their home too and I'm not going to set arbitrary rules about when people may and may not cook. Frankly there are worse things my 18 and 22 year olds could be doing than coming home late from the gym and eating some relatively healthy food.

Can't he microwave his dinner and wash his plate up. If he wants eggs and chicken in addition, he needs to batch cook them at a suitable time and eat them cold from the fridge. Tell him you don't want cooking happening after a set time on a regular basis.

I don't think anyone has said it's not irritating. Yes it's irritating. It's not move out because your step son is impossible to live with territory.

The issue is that he is leaving too much mess and making too much noise.

Explain that he needs to wash all his dishes and clean the sink so egg snot and grimy plates aren't left next day for you to clear up after you have already tidied the kitchen.

Meanwhile, stop buying eggs or porridge oats!

I dont know if it would irritate most parents, my ds1 moved back home for 6 months last year, yes he would eat with us if he was home but if he wasnt home for dinner we would pop him a plate on the side for later
He used to make his own breakfast and lunch, yes it was not in keeping with the time we ate, due to work and the gym and not getting up until late some days, and he defo used to cook at night when I was asleep but I was asleep so it didnt bother me at all

I'd stop buying eggs. Completely.

A 30k income would probably get him a mortgage between 120k- 150k
If with his bonus it's 40k that could be 160k - 200k if a bank would take the whole bonus into account.

If he is not sensible/conservative with his money see if your husband will get him to continue paying £150 rent but insist he puts £500 each month into a LISA (?) the account which you can use to buy a house and get the government bonus.

Low rent is lovely if it helps him save a deposit not so lovely if it all goes down the pan.

Your husband could phrase it £500 each month into a "low risk" investment and insist he is shown the money being saved. Otherwise rent goes up to £650 and your husband saves £500 for him.

I expect he has been sucked in by investment people on youtube etc. Many of these have been exposed as scammers that make their money by charging people to teach them how to invest.

I think a lot of other posters are being unreasonable and I'd bet money they wouldn't like it either. He's 21 years old and cooks 4 poached eggs on toast whilst you're trying to cook dinner. You then put his dinner aside which he eats when he gets home at gone 10 o'clock at which point he also always makes another 4 poached eggs on toast along with porridge. This performance can sometimes be in the early hours of the morning. This isn't once a week or occasionally, it's every night. Yep, that would irritate most parents or even flat mates.

He's an adult and he can eat what and when he likes.
However, if he's living with others then he needs to be considerate of others and that means not making a noise if he is cooking late at night and making sure he cleans up everything, including washing his dishes if the dishwasher is on, not just leaving them there waiting for the next run.

I think it's time he moved out. He can afford it, and then he would have the freedom to run his life as he pleases and the responsibility of keeping his own place clean.

I would get your DH to tell him, "look this is a family house. We don't need a lodger. Either you live here as part of our family, which means respecting our schedule and taking your turn cooking for the family, or you need to find somewhere where you can have more independence."

You’re getting a hard time OP but I totally get why you’d feel like that.

My DH does most of the cooking but I do the washing up, wiping down etc after meals and yes I like to leave it all clean for the night. It annoys me when DH gets a snack and leaves mess everywhere every single time. Buttery knives on the surface, crumbs all over the floor, cupboard doors open etc. I try and swallow my annoyance.

A tidy house for me makes me happier, I couldn’t go to bed leaving the kitchen in a state. I really wish I could but it would make me anxious. Some people won’t understand that. Your DSS is basically giving you the middle finger not caring about how it makes you feel.

Oops posted too soon! You clearly think he has an eating disorder. If he does, he needs help not anger. Men with eating disorders often struggle to get support.

If you know he’s had eating problems I think you need to be a bit kinder

Lots of problems here and YANBU.
He earns well plus commission and pays so little contribution. He blew through and lost money on risky investments which he wants to take up again. He eats far, far more in food from your description than £150 per month, let alone something to go towards the house. He seems to have the timetable and hours of a single man while living as a dependent. Also said he wants to give up work.

Hard no from me: he needs to move out and you need to make sure he moves out so he keeps working to pay his rent and support himself). He does not need to live at home when he is working full time and not in education on this wage.