Average Age of American Fathers Has Increased Over the Past Four Decades

Father and baby

Men in America are waiting longer to start families. The average age of fathers in America increased by 3.5 years between 1972 and 2015, according to a new study in the journal Human Reproduction. Despite variations along geographic, racial, and demographic lines, the average age of American fathers increased from 27.4 to 30.9 over that time. In addition, the number of children fathered by men over 40 doubled in that time.

Despite this trend, the gap between the ages of mothers and fathers has been decreasing over the same period.

Researchers at Stanford University conducted a deep data analysis of live births in the United States to answer the question: "How has the mean paternal age in the USA changed over the past 4 decades?" They studied 168,867,480 live births from 1972 to 2015 and discovered some clear trends.

The study fills a gap of knowledge about trends in fatherhood. Much research has been dedicated to studying trends in motherhood, but this is the first time a similar study has been conducted to track paternal age. As the paper's abstract states,

What is known already: While the rise in mean maternal age and its implications for fertility, birth outcomes and public health have been well documented, little is known about paternal characteristics of births within the USA.

The study found that Asians have the highest average paternal age, while African-American and Native-American fathers had the lowest average age. Geographically, fathers in the Northeast had the highest average age, while the South had the lowest. College education was also associated with higher average paternal age. Despite these variations, the authors say, "Paternal age is rising within the USA among all regions, races and education levels."

Researchers also found that the number of fathers over age 40 increased from 4.1 percent to 8.9 percent over that time, and fathers over 50 increased from 0.5 percent to 0.9 percent.

These demographic changes could have significant implications for population dynamics in America, as well as on the economy. Michael Eisenberg, MD, is the senior author of the study. He is an assistant professor of urology at Stanford University Medical Center. Eisenberg says that there are pluses and minuses to older fathers. Older fathers have an upper limit to how many children they can have in their lifetime, which would affect national population replacement rates. Also, Eisenberg says, "every potential dad acquires an average of two new mutations in his sperm each year. And there are associations between older fatherhood and higher rates of autism, schizophrenia, chromosomal abnormalities, some pediatric cancers and certain rare genetic conditions."

Other studies, it should be pointed out, suggest that genetic mutations are less of a cause of mental health disorders in children of older fathers; rather, fathers with hereditary mental health issues tend to delay fatherhood until later in life. So it may not be clear that mental health outcomes in children are directly affected by the age of the father.