You can honestly never start them early enough imo. I’ve started all mine out just as soon as the gym would accept them. Every gym is different. But it gives them a new network of friends and every gym I’ve been a part of they also give kids time to play at the end of each class…dodge ball or something else like that. It’s really a lot of fun for the kids. I’ve been a kids coach for many years and it’s fun watching them learn and become competitive. There are competitions they can enter if they’re ultra competitive. We have competed in the past, but don’t right now because it’s just too expensive ($100 for each of us to enter). But they’re great ways to test your mettle. A lot of gyms also provide in-house tournaments where the only competitors are those you train with.
My only regret was in not starting these two styles (BJJ and Muay Thai) much earlier in my life. I’m a 2nd degree blackbelt in another form of martial arts (a McDojo style - it took 4 years) and I’ve also trained extensively in Aikido (think Steven Segal). I also trained Karate and Taekwondo before as well. In some form or another, I’ve been training in some form of martial arts since I was 20, in the Army. But I tell everyone…I learned more (and felt more confident that I had the skills to really defend myself and my family) after 1 month in BJJ than I did in all the years I invested in all those other styles combined.
You can never start them early enough imo.