I rushed/pledged as a second semester sophomore at Berkeley, a school where most of the people who rush and pledge are "Frosh". I say go for it. It's one of the greatest experiences you'll ever go through. Our fraternity is even known to take seniors from time to time and have no qualms about juniors.
P.S. Of course, I realize now this is sorority related, but I had to throw in my two cents.
Go for it kid.
