Go to any investment bank. Take a look at every other desk except currency traders. You'll notice the average age is around 30. Take a look at the currency desk, and you'll realize the average age is around 50. Why?

Bonds, stocks, exotics -- that stuff is all teachable. Give someone two years and they can learn to work the markets. Currency has basically zero theory surrounding it. The guys who are really good have no idea why they're good at it. It's basically all just trapped in their heads and they can't get it out. That's why the guys who are good at it tend to stick around forever and they end up being much older than the other guys on average.