I have some skill learning house rules on my blog. They can be found
here.
They're as realistic as I could possibly make them based on the data I could find on human learning.
I made the assumption that humans have a maximum realistic skill level of 20. Which might not be right. It might be fourteen, sixteen, or twenty-five. It's difficult to figure out what the maximum is.
The long and short of it is this: it takes a long time to get good at anything, and being good at one thing doesn't make you better at other things. You can practice the violence for a decade and master the violin, but doing so won't make you any better at chess, brain surgery, nuclear physics, computer programming, or anything other than playing musical instruments.
The
GURPS attributes, which raise lots of skill at once, have no basic in reality. There's nothing you can do that will make you better at all of violin, chess, surgery, physics, computer programming, writing, etc. There's not even anything you can do that will improve any
two of them. That's not how humans learn.