My DS is 3.7 and can't/won't pedal trikes, ride alongs etc. He was late to walk at almost 19 months, and I think he probably still is a bit behind in some areas eg he doesn't run all that fast. But he can jump well with two feet, can climb (cautiously) etc at the playground, scoot (I think) pretty well and is just getting the hang of his balance bike (although he's yet to lift his feet off the floor for any length of time).
Does it matter?