Outstanding article at Baseball Primer, with extensive data and research, comparing the aging pattern for pitchers since the beginning of baseball through those pitchers born in 1968.
Long, very informative article, seeking to answer the question, are pitchers peaking later or aging better?
The quick answer...pitchers are still peaking where they've generally always peaked, ages 25-29.
And while pitchers are aging better now than they did in the previous couple of decades, they aren't necessarily aging that much better than they were prior to that.
The author concludes that the poor aging for pitchers born in the 1940s and 1950s owes in large part to the heavy usage patterns they were subjected to in the 1960s and 1970s...they seem to have held up to it, but tended to fade much more quickly once they turned 30.
However, pitchers are retaining more of their value from age 35 on than they have historically, although generally, as a group, they still aren't close to as good as they were in their late-20s.