There are many, many generations of people who rode bikes as kids without a single bike fitting. I say go for the bike. He will love it! Our office a few years back adopted a whole family one Christmas. My DH and I bought a bike for one of the kids. I was lucky enough to be one of the group that went to give the family their gifts. The look on that little girl's face was worth way more than what we paid for that bike. I definitely got a warm and fuzzy feeling that day.
As we must account for every idle word, so must we account for every idle silence." ~Benjamin Franklin