I could perhaps make an exception for an exceptional 16 year old to be awarded a black belt but as to the belt thing in another dojo, no way, because black belts are not normally handed out that way. As has been pointed out by numerous people on numerous occasions, belts are a mark of progress in any particular system. They cannot be compared style to style. What it would mean, if this kid wandered into our dojo (we don't train in a gym), and could handle himself doing the things we do, is that he is a very competent martial artist. Nothing more.
By your arguement I could wander into an Iaido school, challenge them to a fight by my rules and become an Iaido black belt because I could beat them in a fight that favours me. If it was fair dinkum fighting they could use a sword but because that is not part of my training and they don't really want to hurt me the sword is not part of the fight.
Then another way of looking at your hypothetical is, if I go into an MMA gym and beat an MMA guy, what does it prove? Just that I am competent at what I do. It doesn't make me a BJJ black belt or an MMA black belt if they have such things.
:asian: