Most people don't move out til much later tbh, I didn't leave till I was 24 and still sometimes wish I'd stuck around a bit longer even with paying a big chunk of board, I know people that probably won't move out if they can help it because they're not being charged board etc so it's a total steal. There's a family across the road that clearly aren't charging their lads rent as they're all still at home with cars and trade vehicles all on the front, basically using the place as a hotel but for some reason the parents don't care. That's a bit much for me!
I digress!
I'm not earning 42k admittedly but if he's down south it won't go as far as you think. I'd keep saving. I'd do my late teens/early 20s a lot differently with the benefit of hindsight and saving far more aggressively is one of them.