Furthermore, have you not been reading any of the responses here? Even if the assumption that Pokemon is based on the human life cycle was a fact, it's still stupid to think that somehow that is undeniable linked to the number three, seeing as there are not three set-in-stone stages of the human life cycle.
Caterpillers turning into butterflies is nothing to do with age. It's a transformation that can happen once they've consumed enough sustenance. Furthermore a human being goes through no such drastic process to turn from one thing into another. To compare the two is strange. Humans start young and gradually grow bigger and stronger over time. Caterpillers eat and eat, and then undertake metamorphisis changing into something that looks entirely different. Tadpoles turning into frogs is also a transformation and is unlike the human aging process. Interestingly however, if you look at Poliwrath, despite being at the end of it's respective evolution line it is STILL not a full frog, so it goes to show that it's not just about the standard of things. Politoad may exist, but it was introduced an entire gen after, and it is its own evolutionary final stage, so it is still fully evolved.
Anyway, the point is evolution in Pokemon is clearly not set to the standard of the human aging cycle, else ALL Pokemon would conform to this standard, and they'd likely all be human-shaped in some way. But the even bigger point here is that even if all Pokemon did conform to this standard, it wouldn't change anything because there being only three stages of that cycle is debatable. I noted five stages earlier.