I agree with having some older players in the draft, but I don't think they should have a huge advantage salary-wise over the younger guys. Having guys with like $50k salary coming in the draft completely defeats the purpose of training. You could easily have a 18-yo and a 22-yo with similar skill levels drafted early but still low-salaried. I like your idea of giving them more experience though. Since experience has an "unknown" level of effect on the game it could easily be turned into the "advantage" for drafting older players despite their fewer years in the league.
A 22yo with more experience would be useless to almost any team in this game, especially as long as the impact of XP is unknown and seems to be quite marginal for the lower levels of XP...