I guess for me, Jones, it helps round out the possible life experiences a person may have had, along with other "getting to know you" stuff. (Which is why humans tend to want to know these things, I guess.) Like where you grew up, what sorts of books or films you enjoy, if you ride motorbikes, do you have siblings, have you travelled, what sorts of jobs you've had and other "what type of person are you on the surface" questions. The era in which you grew up would definitely impact on your outlook, as does the area you grew up in.
So, if you married at 18, I'd possibly think that was interesting, to have been so certain at a young age that you'd found your soul-mate. Obviously, your perspective on life would be different to another person who may have married at 35, or one who decided not to marry at all. We are all many parts, and age is but one part. However, we can't really say it doesn't matter, because clearly, it does.