That to a great extent that depends on the country/state/province you live in. In the U.S. there are some interesting exceptions to the 16-year old marriageability age. From our friends at Wikipedia
Canada:
Varies by province, but generally 18 years old, 16 years with parental consent,
14 years with judicial consent.
Mexico: 18, 16 with parental or legal consent,
14 for pregnant females with legal consent.
Puerto Rico:
21 (younger parties may obtain license in case of pregnancy or birth of child), 18 with parental consent.
California:
no statutory minimum, those under 18 must receive approval of a superior court judge, or parental consent.
Indiana: 18, 17 with parental consent,
15 in the case of pregnancy with both parental and judicial consent.
Massachusetts: 18 for first marriage,
14 (male) 12 (female) with parental and judicial consent.
Michigan: 18, 16 with parental consent,
15 and under with parental consent and probate judge approval.
Mississippi: 17 for males,
15 for females, no minimum with parental and judicial consent.
Missouri: 18, 15 with parental consent
New Hampshire: 18,
14 for males and
13 for females, in cases of "special cause" with parental consent and court permission.
Nebraska: 19, 17 with parental consent
Pennsylvania: 18, 16 with parental consent,
14 in case of pregnancy and with the approval of a Judge of the Orphans Court.
Texas: 18, 16 with parental consent.
14 with judicial consent or if person under 18 had previously married and divorced.
Utah: 18, 16 with parental consent,
15 with court approval.
Washington: 18, 17 with parental consent.
May be waived by superior court judge.
West Virginia: 18, 16 with parental consent,
under 16 (unspecified limit) with parental and judicial consent
When I was in high-school there was a Christian couple that were married at age 16. No, she was not pregnant at the time of marriage. I talk to them about it. The did say they received parental permission
and they did mentioned they did not want to spend YEARS (their emphasis) "burning with passion". That was several years ago and I don't know how they are doing.
As for minors dating; it is ultimately the parents decisions if they allow it. I know some parents that forbade it until their children reached adulthood. I known some that have gone the group/chaperone 3rd party route. I have known others that allowed their minor children to date alone.
Which method is best? I suppose it depends. But I really don't know because I have never had children. What is the best age for someone to marry? I don't know; I have never been married.