Growing up I just KNEW I would be married by 18 and was really surprised when I wasn't. Like a few people already mentioned, there seemed to be pressure because you knew that all the good brothers were going to be taken if you didn't get married early on. That being said... I did hear a few elders warning younger ones, including me, to be cautious of marrying young.
I was engaged at 19 after a phone relationship with a 24 year old MS that had only been going on for 3 months! I hardly knew the guy but I had elders call his congregation and check him out and hey, he was an MS so I felt safe. I moved all the way to New York from Kansas to be with him and he turned out to be a controlling sex freak and I was in a strange place with no relatives/good friends to run to. It was a disaster that ended in Dfing, but thankfully I never married the guy and thankfully I figured out that the Watchtower wasn't the truth before requesting reinstatement.
I also had a couple friends that had reached 25 or so and seemed SO old at the time to not be married. I'm 25 now and the thought of that makes me laugh.
oh, another interesting story you may not believe... I knew a girl that got married at 18 I think.. she was home schooled and VERY sheltered even for a Witless. I think she married this guy mostly to get out of the house but he was a MS so I'm sure she felt safe. Shortly after she married this guy she became VERY VERY quiet and they started moving around alot. She had always been a slim girl, but she got really heavy and stopped talking with all her friends. Years later she tried to leave him and he SHOT her!!
I'm from the midwest, so that might have something to do with it to..