Does age REALLY matter?

In United States we have strict laws on age concerning dating and sex, and different laws in different states varies on this matter. The typical age in United States to marry is 18, and that is without parental consent; other states allow that if the teen has a child, that he/she can get married. Laws in other countries are very different, some countries don't have a law regarding the age consent to marry, but the question is does age really matter in terms of marriage. Is there a such thing of being too young or too old to marry? And should we have a international law on marriage?
 In Lagos, Nigeria, a 28-year old Nigeria native married a 71-year old European woman and they said they are deeply in love. What do you think?

These children are from the tribe Yanamamo, which is in the Amazon Forest. By the age of 12, the girls are expected to be married and with two children.

 In rural Afghanistan, an 11-year old girl is set to get married with an 40-year old ma. The young girl said she is sad, because she had dreams of wanting to become a teacher to teach her native language.

 In Yemen, a 6-year old to set to be married off to a 25-year old man.