For me, the right age depends on when I can see myself really settling down for good, and that doesn't appeal to me at all at the moment. I did have a moment of insanity at 21, when my then bf and I discussed rings and such, but at the time I told him to hold off. My parents paid my tuition but were very clear that if I got married I would be a part of my own family and they would no longer offer any financial support. So for me, getting married while still earning my degree would flat out not happen. Period. I'm glad I had that hanging over my head because looking back, if I'd gone through with it I don't think I'd be happy. I take marriage very seriously and if I do get married it will be after a lot of serious thought and a long enough amount of time that we both know we really do want to take the next step.
A lot of girls get married pretty young around here, too. I think for some (and I'm not saying this is THE REASON they're getting married by any means, but...) the wedding excitement and exclamations over their ring blinds them to reality which is that the wedding lasts a day, but the marriage lasts a lot longer than that. Theoretically, anyway.
Then again, though my parents married young (22 and 23), they did it because they had been dating for 7 years and saw no reason to wait since they had both graduated. They've always made it clear to me that they don't give a damn whether I get married or not and that they strongly caution against getting married young unless there is some pressing reason, so I at least don't have any pressure from my immediate family. Extended family though...
ETA: Another reason I don't see myself marrying young is how hard my parents had it after they were married as my father was in a competitive law school on scholarships and loans and neither had any extra money...my mom couldn't get a steady teaching job since no one wanted to hire her when they found out she would only be in that state for fewer than 2 years, so she got by with substituting and working in department stores. That also meant she had to put off her own master's until they'd settled and had stable jobs. They got through it just fine, but I'm not sure I would (handling stress isn't one of my strong points), and for me going to graduate school is not an "if". I would rather just wait until I've gotten my master's and have a stable job.