Joseph, children become adults when they are given and expected to take responsibility. Many lubavitcher Rebbeim married at 14 and their wives were probably about that age as well. A 5 year old who knows shell marry about 12 is alot more mature than the five year old of today.
Even in today’s world, our young adults who marry in their early 20s are much more adult than their non Jewish counterparts who live off their parents through their 30s…