J.B.
My boys were 6, 6 & 4. My step-daughter was something ridiculous like 10. I think that the mistake made with my SD is that my husband bought her first bike waaaayyyy too big so she was 4 riding a bike that really wouldn't fit her until she was 7 or 8, so she hated it because it was so hard. Then her mom also got her a bike that was much too big. Having the bike the right size from the beginning so it's not too hard to ride was, I think, a key part of the younger boys really enjoying riding with training wheels and ready to ride without later.