Courtesy of Foxmad...
1) Arrange friendly for your reserve team against U18's in about 2 weeks time.
2) Select all of your reserve team using Ctrl+A
3) Move them all to either the first team squad or U18's.
4) Continue a few times
5) About a day later you will have a squad full of grey players.
6) All of these will be amazing 19 year old .
7) Offer them contracts and move to Senior team.
8) Another lot will come through.
9) This can be repeated as many times as you like and due to them demanding little wages is a sure fire way to get a better team.