Definitely not too old! I "raced" last year for the first time at 32. Bought my bike (hadn't been on one since I was in college) two weeks before the first race. Had an absolute blast!!! Can't wait for this year.
Out here (Oregon) we have the Cross Crusade Series. They do an outstanding job! Lots of categories, including a beginners category.
As far as being competitive... it all depends on your threshold for pain! You'll be riding for 40-60 min. with your heart rate at the redline! Be prepared and don't expect too much.
Mostly, have a blast!