Don’t remember when - but I was very young. Cannot ever remember NOT riding my bike. Both my kids started when they were 4 - training wheels off by 5th birthday deadline. My first bike was something like this except with a 3-foot sissy bar. Man I miss that bike. I should buy one. Bike riding was much more fun back then. Didn’t care about saddle, pedals, shoes, knee angle, yada, yada, yada… When did life get so complicated?