The idea that marriage should be linked to a certain chronological age is, in my opinion, a bit off. Age and maturity are very different things, and it is maturity that affects our social interactions more heavily, so I would say that maturity should be the qualifier, rather than age. But that begs the question, "how does one measure maturity?" and eventually falls into a jumbled mess of poor and circular reason in attempting to measure an abstract concept. In the end, we can only set an arbitrary age limit (in my opinion, 21) and hope that a person's maturity has kept up with their years.