Youth center level should be used as a limit as to how many youth a club can spawn for the season instead of just how many it can hold. 

Level 1 = 1 player for the season 

Level 5 = 5 player for the season

Holding amount remains the same if they choose to buy youths

Not needed and bad idea.

people must have ability to get new youth to replace their old players

The players market is always there help replace old players. 

Players are the resources of KOB and just like MPL resource need to be limited to be more valuable. 

-100

Young players in the center are 15-16 years old.
Do you mean the center can only train 1 player in 2 seasons?

No, the amount it train remains the same. The amount of new players that can be brought into the game I'm suggesting to be limited 

Terrible idea.. youth purchases are probably the main source of money for global funds, they should be encouraged rather than limited.

Less youth purchases -> lower prizes -> lower demand for new players -> lower activity in the Players Market

Restrictions will make players scarce, player prices will become unreasonably expensive. Buyers who cannot buy them will leave the game.

Buyers who want more players will upgrade youth center. Youths take a minimum 15 season to retire, so even with just one new player per season managers can maintain 14 players squad