I've used Perl since the first release, gotten pretty good at it 5-6 times over the years. . .
That's a bit like saying "I've gotten pretty good at riding a bicycle 5-6 times over the years." Once you learn how to ride a bike, if you go back to it after 20 years of not riding it, you still remember how to ride it.
What I'm saying here is that there is a certain depth of the language that is more in the realm of intuition and nature rather than syntax but yet is integral to the language itself. If you achieve that depth, you never have to get good at it again. But if you never reach that depth, like the two years of a foreign language everyone in highschool is required to take and just a few years later can't remember a word of it, you will have to relearn it almost from the beginning.
So in the same sense, I find Perl to be much like riding a bicycle or learning a foreign language. To really say that you have actually learned it, you need to get to a certain depth of mastery in it.