Some teams can do both, expediently. And in todays game a player can only be young for so long. Considering the duration of a player's career which is averagely 17 to 18 years. A player should be peaking at 21 or 22 years of age. For this to happen,they have to start playing at the top level very early.
So it's never too early to integrate the young talents into the team. Look at what Manchester City I doing with Phil Foden and also what Barcelona are doing with Ansu Fati.