There is a common misconception that in the 17th and 18th century, people married very young—at fifteen or sixteen years old. Actually, the average age at marriage varies greatly depending on not only the time period but the location, and generally it is in the early to mid-20s.
In Colonial New England, 94-98% of men and women who survived to marriageable age actually got married. The average age of males was 25-27 and females 23-25. This is comparable to marriage ages in the 1980s! In Colonial Chesapeake, many males did not marry in the 17th century, probably due to a lack of available women. For immigrants, the average age for males to marry was 25-30and females 21-23. For native-born whites, the ages were younger, 16-17 for females and early for males if they inherited estate (which was quite common).
Sixteen percent of Quakers did not marry. In the 17th and early 18th century, the average marriage age for females was 22-23 and for males 26. The age for females rose by about 2 years in the late 18th century. On the frontier, the average age for females to marry was at age 19 and males at age 21.
In the late 19th century, a slightly smaller percentage of men and women married. The average age for females was 23 and for males it was 27. There was also a decline in the number of children born to families. Couples who married during the 1870s had an average of 2.8 children.
From the 1880s through 1960 there was a gradual decline in marriage age. By 1960 the average was 20.3 years for females and 23.4 years for males. By 1990 it had risen again, to 25.4 years for females and 27.6 years for males.
In the Colonial Period, average American families had six to eight children, and one in four families had 10 or more children! The standard way to estimate children's birth dates is to assume the first child was born about one year after marriage and subsequent children approximately every two years. This is helpful to get a general timeline for a family and to count backwards if you only know the birth date of one child.
By knowing the average age at time of marriage and the average number and spacing of children, we can better analyze previous research to spot possible problems. For example, if dates show a couple was very young or very old at the time of their first marriage, there may be an error. Likewise, children spaced less than nine months apart or more than three or four years apart may indicate a problem with dates or a missing child. Having many more children than average may indicate a second marriage or blended families (especially common in the South).