True, because back then, people had a shorter life span. My Grandma was 16 when she married my Grandfather. They were together until he died at 83.
We have WAAAYYY more access to information at a very early age and that information tends to keep young minds open for more, rather than induce a decision about what their life will or should be.
As ststed previously, a boy of 16 - 20 pretty much knew what he was going to do in life and had a fair grasp on what would be required of him to be a husband and father.
The nuclear family was closer geographically and more often than not, older brothers and sisters were there to help (both young boy and young girl)
I think there is validity to teenagers marrying if they have a strong faith community and family.
A 16 or 20 year old guy has more testosterone than 4 "mature" men of 45 and they can tote that barge and lift that bale a lot longer and quicker than TWO older workers.
And best of all ... they KNOW EVERYTHING and are INDESTRUCTABLE !!!