It's a very individual thing, my DS1 was riding aged 4 but not without training wheels until closer to 5. DS2 was 4 without training wheels and boytwin lost his training wheels before his 4th birthday and is already doing stunts like his fete up on the handlebars when he rides. Girltwin on the other hand has shown no interest and can barely ride with training wheels at 4 years and 8 months. For a 2 year old I would recommend on of those balance bikes with no pedals, he will still be able to go fast but it will help him learn the basics before he is pedalling.