10% is way too little!
When I got my first job, I paid half my wages to my Mum for bed and board, and I was only paid the NIC limit at that time which was £32 per week back in 1983!
As my wages increased year on year, I continued to pay 50% right through until I left home.
Out of the half I kept, I bought my own clothes, so the half I paid was to cover most meals, laundry, bedding, and a place over my head.
I didn't begrudge a penny of it, because I could still save out of my half towards moving out after a few years whereas if I'd moved out earlier, all my wages would have gone on flat rental, food, etc., with nothing left over.
After a couple of years, I took a "loan" off my mother to buy a car, and I paid that back monthly too - I was happy in that she didn't charge me interest, so the monthly payments were less than if I'd got HP or a bank loan for the car.
I think it's good enough that parents give a "hand up" to adult children, rather than a "hand out", as it does make adult children "grow up" and be more responsible a lot sooner than just giving them an extended childhood by giving them too much when they should be capable of being semi self sufficient themselves as adults.