Here's the thing, if someone asked me the following questions:
Was Jeff Weaver overused as a young pitcher?
My answer would be yes based on his high pitch counts and high PAP amongst other things.
Was Jeff Weaver's heavy workload as a young pitcher a prominent factor in his recent struggles? (note the use of the word "prominent", I didn't say "main" but wanted something a little stronger than just "a factor")
My answer would be I don't know but based on the fact he has been able to throw almost 450 innings (6th most) the past two seasons and his VORP of 62.2 is the 37th highest in baseball I would lean heavily to the side of no.
The thing is if players peak around the ages 26-28 on average then just by random distribution there are going to be pitchers that have their peak years at age 23,24 and 25. Griffey had his peak years from age 21-24 but nobody makes the conclusion that his heavy workload as a young player contributed to his "relative decline" after age 24.
And I only pointed out the mistake in years because you have made a pretty big deal about it being specifically "under 25".
I know it is your passion and you have spent a lot of time looking at these things which is why I feel almost obligated to throw some rocks at it to see what holds up and what falls down
