We need to run a test - 18 year old 5* (1 skill point away from 6*) vs 22 year old 6* scout (1 skill point away from 7*) and give them both enough packs to 8* and then 9* and then write down how many green packs both players used to get there. Then we can find out whats better choice. Possibly the 18 year old since you will get 4 more seasons out of him.
You have to remember scout player starts 75 skill points ahead of the 18 year old.
I will do this at the beginning of next season when I have tokens available and also be buying a few new players.
If I remember approximately it cost me about 500T to get a 23 year old scout all the way from 6*89 to 9*100 in Level 13.