UFC is about way more than being strong and in shape. You have to be a crazy motherfucker who is immune to pain to get anywhere.
If I had the same body and skills as the best UFC fighter, I still wouldn't be able to make it in the UFC, because I'm just not the kind of guy who can dish out, much less take, an ass-whooping.
P.S. How old is your little brother, 13? My stupid cousin thought he'd be an awesome special forces sniper because he played Halo. But that's partly because he has some sort of mental disability (I don't know the official name for it, but its symptoms can be summed up with the words "makes kids into annoying little shits who act 13 regardless of their age.").