Size does Matter.
This thread is starting to look a bit like This thread
here but it's good to see people here have a better grasp on the place the human race is at.
Now, I hate to come across like I'm bragging online, it gets mixed in with all the bulls*** (not pointing any fingers), which isn't nice when your being honest.
I come from a family of boxers and martial artists, and at a younge age was exposed to competitive fighting.
I began training in Tae Kwon Do at the age of 7 with my mother (minumum age at her school) and moved on to the less 'sportsy' and more martial arts side of things with in a few years.
At one point I was state (no-gi) grappling arts champion here for 4 years running, am now a qualified instuctor (not as a living) and have trained in styles such as Tae Kwon Do, Muay Thai, Boxing, Karate, Capoeira, Judo and a few forms of Kung Fu, but have found myself drawn to the grappling arts, such as Kempo Ju-jitsu, Vale Tudo and especially Brazilian Ju-Jitsu due to their general effectiveness.
Anyway, my point is this, I have some experience when it comes to fighting.
I'm not a big guy... about 5'3, but have not always been significantly shorter than others of my age group.
Despite unshakable dedication to the martial arts, I had no choice but to watch as my peers grew taller and heavier, and ipso facto, better fighters than I ever will be. No fault in my technique, it still wins me a spar on regular occaisions.
In no way is weight a deciding factor in many fights, but it is a definate advantage. Any serious competitive fighter will tell you that. This is why all martial arts / martial sports / competive fighting competitions are devided into weight.