A little after turning six. I had training wheels for what seemed like forever. I really wanted to try to ride without them but my dad was hesitant to take them off. This despite the fact that they were coming loose and weren't even engaged a third of the time. Then I saw my one of my friends who was just a couple weeks shy of his 5th birthday start to ride without his training wheels and that was it. I was going to take them off myself if I had to! I got out the wrench and was in the processing of getting the first one off when my dad caught me. I think he figured if I was that determined, he'd help get them off but he gave me the dad lecture that if I hurt myself he wasn't to blame. I did alright. I think I only fell a couple of times with minor scrapes.
Everything in moderation, including moderation.
2007 Rodriguez Adventure/B72
2009 Masi Soulville Mixte/B18
1997 Trek 820 Step-thru Xtracycle/B17