You have to buy players who are between the age of 18-22, those are the best ( of course buy young players that have at least 4 star)
Take an example from me, I haven't play Top Eleven for near 3 months, now I'm back, I have buyed young and even oldest players with 45 star quality and now I'm 2nd in the league.
I have buyed older players becouse I have not many token's by that time so I could "fight" for a young one.
But the things have changed, now I'm buyng just young players between 18-22 and they are the best, they train hard and faster.
Good luck rebuilding your team !