Both of my older children had pedal bikes with training wheels by the time they were about 3. It took around 6-ish months of practicing most days, for them to figure out the way they need to move their body to get the bike going and how to steer and move it. They both were able to ride without their training wheels by the time they were about 4.5.
My DS2, on the other hand, only just turned 3 in Jan, but has no interest in a pedal bike at all, won't even sit on one, and won't ride his balance bike or tricycle. He does love his scooter and is getting better at scoot-ering.