I agree, you can't measure experience by time, but I don't think the number of maps can do the job, I mean, you can make thousands of maps, but if you keep doing the wrong thing over and over (doesn't matter if its artictic or cartography mistakes) you won't grow your abilities, while someone with four maps, who studies, and goes for information, will make better maps with less maps. It also counts your learning speed and your interest for the subject, some people may like to draw maps and create worlds, but i doesn't mean they like geography and if they find the How to get your rivers in the right place tutorial boring, they may never know how to place their rivers

But considering someone with the interest to learn and make correct maps, I think the number of maps will make you grow more the artistic "side" than the cartography, because the first one needs more training, while the last one needs more knowledge. That is how I see it.

Jax made me remember of something I read a while back: Life is growth. If we stop growing, technically and spiritually, we are as good as dead. Morihei Ueshiba.