L.P.
My son learned to ride his bike without training wheels at 5. He was ready, and wanted to do it. And he had no trouble at all. I'd say it definitely depends on the child's attitude toward it. If he wants to try, let him! My cousin's son learned when he was barely 3... my cousin and I were coaching her daughter's cheerleading squad, and her sons were riding their bikes in the school parking lot where the practice was... and the little one jumped on his big brother's bike, and just took off! My other cousin's son only just learned at 8... he was scared and didn't want to try. So it totally depends on the readiness of the child.