My son had almost no inclination to learn to ride a bike even whilst at primary school. When he was 3 he had a pedal powered jeep that he loved riding and would take outside almost every day. Eventually he outgrew the jeep but for some strange reason took no interest in bikes. We bought him a bike with 16 inch wheels but he was very reluctant to even go outside and practice.
Only when he was HE at 13 did he show enthusiasm for riding a bike. He selected a lightweight BMX that cost nearly £200 because he thought it would be the easiest bike to ride. Despite having balance and co-ordination problems it only took him two days from buying it before he was riding it. He practiced in an empty car park using a similar method to that
described here. I particularly like the bit mentioned about BMXs with 3-piece cranks. My son's BMX is fitted with them and they were detached when he was learning to ride then re-attached when he thought he was able to use the pedals. I think it would be a sensible move if all children's bikes were fitted with them.
My son has been out on his bike most days since he learned to ride. Initially he would only go out locally during the school day to avoid encountering bullies from school who might nick his bike, and he would ride outside the locality at weekends.