I can't see any age being optimal for marriage. My pastor back home married his wife when he was about 19, and they've been together over 50 years now. On the other hand, a former coworker of mine married at 37. Depends on you and the person. Can the two of you adequately handle stress, communicate well, resolve or tolerate those pesky things the other does, etc.?
Personally, I'm waiting until I finish college and get at least some kind of job going. I don't plan on being single forever, either. I would reckon the prime marrying age is somewhere between 25-35.