Gareth Bale? Thierry Henry?
WHy are you naming those players and in what context?
Bale made 43 appearances for Southampton at 17, 12 for Spurs at 18, 30 for Spurs at 19, 34 at 20.... etc
Henry made 2 appearances at 16, 8 at 17, 22 at 18yrs old, 48 at 19yrs old, 44 at 20yrs old.. then 38 spread across two different clubs at 21years old and 47 appearances in his first year at Arsenal at 22 years old.
So... were you suggesting these were two players who didn't play much by 19? Because it seems to me Henry played 78 games before turning 20, and Bale played 82.
DO you think Henry would have burst into big form with Arsenal at 22 had he not already played some 160 games before he joined Arsenal, I don't think so. What about Bale, do you think he'd have been sold for 80mil, if he hadn't played 248 games before he turned 24?
This is excluding internationals, which for both players isn't a huge number but still experience, add in under 21 national performances and those numbers would increase further still.
You named two guys with a huge number of games before hitting 20, the best players start playing at 16-17 for a reason. They are better at 17, they are better by 20, they are better at 28 than other players. better players are better, age doesn't really come in to it. Great players are rarely not worthy of first team games by 19, the number of players who ended up great who barely played till over 20 is very very small.
If they are actually brilliant when they start playing doesn't matter all that much, it's games, experience, improving. If you aren't getting games by 19, where is the improvement going to come from when other players are getting games at that age? Bale wasn't brilliant at 18 and 19, and 20, but he showed potential, and to be the player he is today required playing those 200 games previously at the key ages.
Look at how many players at Arsenal/Chelsea/Utd who DON'T play much between 18-23 end up leaving, stagnating, never improving beyond their potential they showed at 18-19 and end up in some non league team or maybe league two.