farm rest booster everyday, don't use it, keep it for next season.

start new season, train only 3 Fast trainer (18 yr/o) until they reach 120% by using the rest booster you have collected.

then, make sure to put this 3 players on 1st 11 every match, they will gain skill every match and at the end of season, they will reach 140%.

start again new season, those FT will reduce to 120% (19 yr/o),

and then find another 3 fast trainer, train this new 3 fast trainer (18 yr/o) until they reach 120% using the rest booster you have collected everyday.

keep repeating this step. after 4 season, you will have 12 fast trainer (120%) squad you have trained with maximum age 21 yr/o