It all depends on your server.
How many tokens do you need to buy a 18 years old player at your server today or in the next days?
Compare your youngters to one of your players to see is market value, and see If he really is a fast trainer or not, the price in token does not represent the training speed.
In the last 2 seasons i received 2 youngsters 3* players 1SP for next star, both for 15T and they are the fastest trainer you can get 14,5m and 19,3m for level 8 and 9.
I signed both, because i Never saw any player on server with there market value.