I think its much less defined when kids move out around university these days.
I moved out at 18, spent a year on an internship, then went to university. I only had term time accom so had to come home for the holidays.
Then lived at home for a year and a half after finishing uni, before moving out again into shared accommodation then finally private rented.
Some people were very odd about kids coming home in the holidays, presumably not realising that lots of university accommodations are 52 weeks a year. People tend not to realise the way grants work these days means its based on parental income so parents are expected to financially support you at uni (and you can't loan more money). My parents were iffy about me moving back in after uni, until I explained the amount of overdraft I was in, and the amount expected for a deposit these days.