One big issue in genealogical research is determining when a couple got married. There seems to be an illusion that once people hit the American shores, marriage age hit the mid-teens. In some cases that may have been true, but as a general rule couples followed the customs of their homeland.
In Great Britain, the average marriage age during the 17th and 18th centuries was about 28 for men and 25/26 for women. There were exceptions, of course. Some married a bit older, some a bit younger. As generations passed, the marriage age tended to drop. By the 20th century, couples were marrying in their late teens or early twenties with greater frequency than their immigrant ancestors.
Circumstances could play a roll in the marriage as well. If a girl was "with child" and in her mid-teens, a quick marriage could be in order. The husband could be anywhere from 16 to 50 [or older]. Play around with an age gap like that in early census records!!
There were cases where girls and boys married in their early teens [think Romeo and Juliet] and nobility had their own set of customs. Most of the folks who came to America from the British Isles were a few generations removed from noble bloodlines, if they had any at all.
In looking at my early Land ancestors, marriage ages vary a bit. They are also estimates for the most part:
Francis Land & Frances _______. Francis was born about 1604 and they married about 1638, when Frances was 24. Mr. Land was an exception to the rule, marrying younger than 28.
Renatus Land [b. c1641] & Frances Keeling [b. c1646] married c1665. Renatus would have been 25; Frances 19. Once again, the couple violates the rule. Especially Frances!
Robert Land [b. c1672] & Phebe Bonney [b. c1684] married about 1700. Robert holds true to the average, but Phebe really breaks the trend at 16.
Edward Land [b. c1710] & Eleanor McClanahan [b. c1715] married between 1730 & 1734. This couple really pushes the envelope! Edward would have been 20-24, Eleanor 15-19.
All four generations are working on estimates for birth and marriage years to this point. As a result they may not be terribly good examples. Additional research needs to be done on all of these families. A check on marriage customs for their particular home shires needs to be examined as well.