When my #2son was 4yrs, he came tramping through the house with a wrench. Where ya going with that kiddo? I'm gonna take those stupid wheels off my bike. And he did too, with just a little help finding the right sized wrench and getting it a little loose.Once we took the training wheels off my younger sons bike he refused to ride it.
#1son didn't want training wheels. He was better off hanging his feet on either side and didn't like it when we tried the training wheels, so they came off really quick. He was tall though, so his feet could touch easily.