There are great videos of a Swedish three year old on a half pipe on a balance bike! My kids were not so fearless, but my son did a 8 mile ride (flat ex railway line) on a balance bike when he was 3. And before anyone accuses me of pushy parenting... we didn't make him! The plan had always been for my wife to ride with him separately, but he insisted on coming the whole way with his two siblings. It was a really memorable day.