How do those kids fight mma?

I was under the impression that you had to be 18 to fight a legit mma match like that?..That video thats floating around here just made me wonder

now with that being said, im all for kids mma. Those kids showed very impressive skill sets and just comes to show you how far this great sport has evolved from the likes of tank abbot. I feel kids mma should be allowed on the amateur level and dont see why not

soo is there any info on how this can take place...are there places that let u fight at 17 with a waiver?