I’d say age isn’t as important a factor as life experience.
If you’ve dated several people that gave you a well-rounded understanding of what you would need/want in a spouse, and are ready to be independent – which includes having received as much education as your vocation necessitates, then you may be ready for marriage.
I read somewhere (Matthew Kelly maybe?) that people marrying young shouldn’t be frowned upon, necessarily. If the couple truly believes it is meant to marry, then why wait? I look at this idea with reservation, because who is to say an 18 year old is mature enough to understand true love? (Heck, some 50 year olds don’t understand it!)
That’s just my take. I got married at 25 and the timing couldn’t have been more perfect.