Won't give you a graph Mets Fan but I'll throw some hard data at you to hopefully show what I'm trying to emphasize.
Using MLB.com stats to simply look at the top 50 pitchers in the MLB last year based on ERA and qualifying (all have minimum 160 innings pitched).
Ages 2011 Top 50 MLB Starting Pitchers
Major League Baseball Stats | MLB.com: Stats
Average Age = 28.72
# of pitchers aged 30+ = 18
# of pitchers aged 33+ = 10
# of pichers aged 35+ = 6
As you can see there really are not that many guys 30+ and into their mid thirtys that are "top pitchers" IRL. The average age of a top pitcher in his prime last season was right around 28. and while certain pitchers can pitch well once they get to 33 and over in age there are very very few who actually can. Guys like Halladay, Lee, Hudson, Dickey, etc are all rare exceptions.
Interesting enough when looking at the same spectrum of data for my Modern Day MLB League in 2036 (.375 ageing, .900 Dev) Average age of the top 50 pitchers by ERA the average age is actually slightly HIGHER!
Average age = 29.26 so slightly higher
# of pitchers aged 30+ = 22 slightly higher
# of pitchers aged 33+ = 10 spot on
# of pitchers aged 35+ = 4 slightly lower
So as you can see all the age distributions for the top pitchers in the league using this setting, VORP, and I assume WAR as well will all measure out close to real life. For whatever reason, top MLB pitchers are trending younger and that's why there are a vast amount of top aces in the game.
Now with that said there most likely is a lower distribution, although I wouldn't say major but somewhat there, of older pitchers throughout the entire league. However, that's something I have to live with because as I said before if you crank down the Dev settings or age modifier guys start hangining on too long and there's too many good 33+ and 35+ top pitchers in the game. I would go through and check year by year periodically and I counted 50-55% at times pitchers aged 30+ in the top portion of my league which is off from real life. My personal preference is to take a top down approach when it comes to this stuff as I would rather get the that right than have my league dominated by older guys etc.