I was just going to say - doesn't it also matter what one's purpose is? To be an Olympic competitor? To be able to kick above his or her own head? Or to be able to surprise a back alley mugger? All different goals, all variously dependent on one's natural athleticism, genetics, and training.
I am five feet even (that's not "short" - it's "gravitationally superior"), with bad hips, bad back, some arthritis in both knees, multiple concussions, and a messed up spine. What I can achieve with training is limited - because some kinds of training are so unbearably painful to me they lose all effectiveness. However, I can compile my own training program, where I can become effective and proficient. I will never be an Olympic competitor - that's ok. I will never be able to kick anyone in the head, because the amount of pain that will cause to me will knock me out - which sort of defeats the purpose of kicking my opponent.

But can I get to a point where I am an effective self-defender? By all means. Very reachable despite my limitations. And, possibly, better than other people BECAUSE of my limitations.