Any labels that one puts on themselves are limiting us, especially when they supposedly apply to our intrinsic qualities. I would say that there are certainly people with different levels of a need for interaction with other people and I would say that a sizable chunk of that is dictated by our innate personality, not just our situation and prior experience which surely play a large role too.

But I absolutely agree, labeling yourself as either one is a useless act that can easily do more harm than good. And if you want to measure something like that, don't view it as something binary, but as a spectrum and it's a spectrum one could certainly move along with time as you suggested.