It's about 2 green boosters/skill point for a 6* player aged 22-25
It's about 3 green boosters/skill point for a 7* player aged 22-25
It's about 4 green boosters/skill point for a 8* player aged 22-25
It's about 6 green boosters/skill point for a 9* player aged 22-25
Once a player turns 26 there development slows.