It wasn't just living in an ordinary house, though. We had the equivalent of a three roomed flat, as they lived in an old Victorian terraced house with three floors and seven bedrooms. It would probably be condemned now, but they sold it to a housing association which turned it into bedsits for 16-18 year olds coming out of care.
Most young people carry on living with their parents until they have enough money to move out. It's just being part of a normal family.
Jess's OP was about those who cannot for one reason or another.
If my parents had had the sort of house that many people live in, we would not have been able to live there.
By the way, I was 17 when I got married and had my first son.