No reason you shouldn't be able to enjoy skiing even starting late in life.
On the other hand, i never met anyone who started after 20 and is a very good skier.
Hmmm...my initial reaction was that you've got to be wrong about this...but then I thought about surfing, which I learned in my early teens, and how many people I knew who took it up later in life and how good they were. And I think you might be mostly right. There's just something about how easily and deeply you learn movement patterns when you're young.
I guess it depends on your definition of "very good." I'd say a very good skier can ski the whole mountain plus out of bounds while being in control and with fluidity. So surely there are many, many people who started skiiing later who meet these criteria. But if your definition is "near-sponsored free skier or college-level racer," then I think you're probably right...