Young players aren't worth more "because they improve more",
Jason, you are here? (And you know why i am saying this.....) Anyway:
I am surprised by what you say because older players are closer to their 99max-ratings (Paul once told me that ALL ratings in the FWL have a 99max-potential) and therefore improve less than younger players.
And even if the actual rating and the given TC-percentage for the skill is the same, a younger player usually gets a better improvement than an aging one.
So i would say that young players improve more. It can be seen in any TC we have done yet.