I was in my mid-twenties when I got it done for medical reasons. I had a condition called phymosis which in my particular case was the result of the foreskin being fused to the glans.
Despite the amount of pain I was in for about a week and a half after the fact, I'm still glad that my parents choose not to mutilate my genitals as a child. I'm all for body modification, but the choice should be left to the individual who has to live with the results.
Funny, tangentally related bit of TMI -- as if this post wasn't already -- despite several different sex partners, the occasional STI exam, and just regular check-ups, the first person to point out to me that I had an abnormality was because it was preventing me from getting a piercing I wanted. So I was already planning on getting muilated, just not quite that way. Of course, piercings don't hurt as much, and heal a whole lot quicker.