Dave Winer on that dumb thing Mark Zuckerberg said when he was 22:
My own experience: I did great work when I was in my 20s, 30s, 40s and 50s. The stuff I'm most famous for I did in my 40s. But the best software I've ever done was this week. I think that's pretty much been true all the way through. It all builds.
I hope this is always true for me, too. The day I start thinking the code I wrote a month ago is still good will probably be the day to hang it up.