I was probably 7 or 8. Until the age of 6 my parents used the third wheel, too. I guess, to protect me from falling and hurting myself. They probably thought I was too small to ride a bike normally. Maybe they were right, I don't remember anything in details.
In the fall, I wasn't successful enough at riding my bike without any support. I was falling, actually. So, fall probably not the best time to learn how to ride. But in spring, however, I finally succeeded.