@Oziris92 This is a good question. Because if you look at it this way. Its Youth and Senior.
I would presume Youth means the youth team, under 18s.
The Senior would be the senior squad. Setting it to normal or whatever the usual rate is doesnt seem to work very well for the senior squad. It takes 24 weeks to have a 19 year old gain a level and 5 weeks for a 31 year old to gain a level.. This appears to be broken.
Ive played the same RB in every match for 5-6 matches in a row and his Match XP is low. Really? How is that possible. I think starting every career with everything on fast is the only way to go because I do not thing the normal setting is actually working, then again IM not sure the fast setting is working either because the youth players seem very slow developing as well. Unless there is some massive development push after a season is over.