For comparison, big wheels were advertised 4 - 9, so quite a bit younger range. But there was also a little wheel for 2 1/2 - 4, and a mini wheel for tots 1 1/2 - 3.

For bikes, pediatric groups have fuzzy ranges and say most children learn some time between 3-9. Random web site claims ahead -> The fraction of children who learn to ride a bike is 75% (UK numbers) where their parents were at 95%. The US was on a similar trend, but since 2018 it has reversed, and there is a surge of children (and adults!) riding bikes.