I am of firm belief that once a person has reached the age of comprehending all the responsibility and hardships that marriage holds- they are old enough to marry. It can be at 16 and it can be at 30.
That said, I find the idea of wanting most/all people to marry off younger in this modern world highly unrealistic- most couples, especially younger ones who marry before the chance to finish college, need two incomes to survive. One partner staying at home raising a baby is highly unrealistic if the other one is 18 and not college educated. More likely than not, these marriages lead to neglected children who spend all day in child care because parents need to work, or it causes so much drama that a divorce happens. This is not an ideal situation to raise children in.
Marrying later implies financial stability- which is very much the ideal. Waiting until one or both partners receive a college education can assure thriving as a single-income household, allowing one partner to stay at home and raise children.
That said, there are some cultures that make it work- I would think that the Old Order Amish are a great example of this. Amish children, boys and girls alike, begin working after the 8th grade, and there's alot of communit support, which is hardly present in the city lifestyle. The early exposure to labor as well as a strong sense of community and obligation negate divorce rates and ensure family survival- making it a viable and likely option to marry and have children at a younger age.
,Shel90.