My 13 yo son wants to take and compete in a martial art. He wants Judo, BJJ or Muay Thai. I am ignorant on the subject, but it seems to me, his physique would suggest that grappling is not for him. He is 5' 10" and weighs less than 120. Long and lanky, it seems to me, is not good for BJJ and perhaps even Judo. Should I steer him towards Muay Thai?
This is for sport.
In my experience, Sport makes for better real-world training than anything else anyway. Let him do whichever appeals to him more. I've dabbled in Muay Thai and spent a few months practicing Judo and BJJ together and you can't go wrong in any of these areas. I'm about 5'9" and I excelled in Grappling more so than striking, although I've spent most of my time in Martial Arts doing Boxing and a few years in Kung Fu when I was younger. I'm currently enrolled in Judo because it's the cheapest of all the above mentioned, but I'd like to move on to a full MMA school.