Has anyone had a 22yr college prospect who has gotten close to his Proj rating? 
Can you expect a 22yr old to jump up from 65 to 90 in 5 seasons?

Yes
Marginal at best

With a little more detail-- 22 yo college prospects grow a fair bit, but 25 points in a category is probably more than 2 standard deviations above the mean for them.  Even if you have $20M in scouting, I'd temper my expectations some here.

How about this case:

A 22 year old who is currently at 72 overall, projects out to 90 w/a $20M college scouting budget. 

His biggest reach is his glove, needing 27 pts to hit the peak projection. (65-92)  Most of the rest of the projections lack about 15 pts of reaching their peaks, but there are a couple of others that are 20+. 

My rule of thumb is I estimate a 17-20 point increase in each category, depending on what it is.  Do others have similar ideas, or am I way off base here?  

With a 100 make up, good coaching and aqequate playing time, its possible.  I checked the best players in my world, and a couple have achieved 20-25 pt improvements.