Alta - one thing about skiing and the plateau has to partially be due to the speed/risk factor. You and I both started skiing as wee pups, and maybe can't relate. But crossing to the next level in skiing probably means taking risks that make you leave your comfort zone. I'm petrified of heights and that falling sensation, yet I feel so comfy on skis I don't even put height/falling together with skiing - even on a chairlift. I just go. But if I was intermediate at my ripe age of 40-something, it'd probably be pretty tough to let my body go straight down the fall-line and rely on a metal edge. Whereas, if I was a intermediate golfer, may have to do stuff that's new and different to get to the next level, but I wouldn't be 'scared' and putting my body into danger, kwim? I think that's a big difference between skiing and other sports.
Well- I'm learning speed skating right now - and I think with any sport where you're moving, you've got skills to learn that involve fear and committment. Doing those first crossovers in the corners on speed skates was terrifying and I felt almost paralyzed with fear (and that was going like 2mph). And a couple months later, now I'm flying around corners leaned over and I at least have moments where it's feeling pretty darned comfortable.
I don't doubt that it's coming easier to me because I can feel where some of the motions are similar to skiing and I'm generally comfortable with speed. I'm sure that most things are easier to learn if you start young. But I guess I just don't believe in focusing on limitations that you can't do anything about and may or may not exist.
If you tell yourself, I can't get comfortable with speed because I didn't learn it when I was young... well then it's definitely true. If you believe you can learn to get used to it - that's probably true as well.
I mean - when I had my first knee surgery - I had a lot of people tell me how my knees would never be the same and I'd probably never ski the same again. Which I ignored and ended up skiing better than ever after it (after each one, actually). Which is not to say that my knees are the same - they definitely have some issues and while I have to work around those issues, I've chosen to ignore the percieved limitation and decided that I can learn to ski better if not harder, and I think that helps a great deal. I think it's one of those types of things. Sure, it might not be as easy to learn to be comfortable with speed when you're older. But it's not impossible unless you believe it is.
Basically - I do get what you're saying. I know in reality, everything is easier if you learned it when you're young - especially where fear is involved. But I personally believe those types of 'facts' are best ignored. ;)