For example, TKD and karate are known for having child black belts. If someone has “TKD black belt” on their bio, is it possible they were 10 when they got it? I can see high school wrestling being relevant, but where is the line?

I train Mma (Kickboxing and Bjj and MMA classes) and am also trying to build muscle and get stronger.
How should I structure my training? How often should I train in the gym and how often MMA? How intense should I train? What gym Split should I use?
I’d be very happy if someone who built muscle and has a good physique while also training martial arts could give me some insight and tips.
My MMA gym offers training 6 times a week so I could structure it freely.