Is there an age limit to music success?

Every once in a while I'll visit my family. When I have some off time from working and art, it's good to catch up on things and overall, relax with them. My lil bro subscribes to Alternative Press magazine. Most of the magazine features the same garbage and columns with whatever the flavor of the week is. They always seem to have their fingers on whatever Fall Out Boy is doing or whatever Myspace sensation is tearing up the web. Well anyways, I came upon an article/poll about musicians and bands being too old to play...Is there an age to success in the music world? This could be a toss-up. If you're 43 years old, still dressing up like you're 18 playing the same music aimed towards teens, you'll look like a desperate wanker. But if you're playing what you love, how can one condemn that? AC/DC has been around for a very long time and continue to play what they love. The fans dig it and no one is unhappy.
But then again, they're iconic. They're classic. You can't match up groups like AC/DC with Cobra Starship or any of those groups that are painful to hear.
But then there are those groups like Bruce Springsteen and the E-Street Band, The Rolling Stones and Tom Petty and the Heartbreakers. These guys don't look like they're having the fun they did when they climbed the ladder to stardom. Sometimes it's good to step away gracefully, then to stretch out your career into complete and udder desperation.