A good friend didn't learn to ride a bike until he was 12 or 13. He lacked the balance necessary until his early teen years. Now he does that Parkour thing, so he outgrew his clumsiness quickly... Just don't pressure the kid, but give him access to a bike he could ride if he wanted to... and eventually he'll want to try it out.
Personal experience, though, I was biking when i was like 4 when my older brother decided i needed to learn to ride a bike. fond, fond memories...