My son began on a OSET at 3.......at 5 he graduated to a PW50, and now Outtacontrol's son has the OSET.
They are a great tool for learning to ride. Unlike the Walmart electric bikes that have an on/off switch for a throttle, an OSET teaches kids throttle control, analog braking techniques, countersteering etc.
When out on the trails on my mountainbike, I couldn't keep up with my son on his OSET.