It doesn't matter; everyone learns to ride. Balance bikes are a fad. No one can't ride because they had training wheels, and in fact the great Amercan cycling boom of the '70s was built on training wheels, so it just doesn't matter if we're talking about learning how to ride a bike. And that happens instantly, by the way, when the kid wants to. You'll spend about 30 mins coaxing them along, then boom, they're off. Personally, I'm more concerned with kids having the intellectual development to be aware of what they're doing and their surroundings before they're zipping around the world on a bike. A suburban cul de sac is different from an urban sidewalk or a country road, so I'm not speaking categorically here, just noting I've seen some kids, including my own, riding in conditions they weren't ready for. Nothing bad has happened, but as a parent, you worry...about their safety, but not about learning to ride.