That is 1-1.5 seasons playing the guy at starter every game. (so 30+ min a game)
For the higher leagues where youngsters don't usually get to start right away, it can take a lot longer
not every game, but 48+ minutes in a week, I think it's ok. They can pop-up even earlier, if they play for example in NT/U21 matches, or in a lot of cup/league games.But, definitely NT/U21 games give them more experience, like other games.