My lad was on a balance bike age 2.5, and onto a bike with pedals aged 4.5. Took 20 minutes to get the hang of it, and 40 minutes to be confident. Had some practice on pedal toys at Nursery.
The key is motivation - he saw his Dad come home from work on his bike every day, and had a fantastic time on the back of my bike aged 1.5 on holiday. Cried at the first stop as he thought the ride was over! Now loves his rides with Dad on Saturdays. 6.5 miles, but with several stops, including one for ice cream.