Age-Old Dads

Do you know how old you are?

I’m 33. Specifically, I’m 33 years, 29 days old. I don’t know the time of day that I was born, but my mom probably remembers within a couple of hours. My dad did not keep track of my age. Growing up, it was normal for him to take me to a sports registration event and need to ask me for plenty of my details in order to complete the paperwork.

Do you know the age of your children? Is it normal for parents to lose track? Or is it just the dads?  …Or just my dad? I have no idea what is typical.

But I do have some decent evidence that, had my dad lived in 1850, he would not have been such an anomaly. Consider exhibit A: A histogram of US ages in 1850. The population was only about 23 million at the time and we have the age for about 19 million of those people. So the graph is relatively representative (IPUMS census data).

Do you notice anything weird about the graph?

That’s the question I asked my Western Economic History class.

First, obviously, some folks in 1850, apparently, thought that they were 185 years old. I don’t know if that’s a record keeping error, insanity, or silliness otherwise. What else do you notice? The bars seem to be periodically high and low well into people’s 30s. This means that there were a lot of people at some ages and a few at others. And the pattern is regular.

Why? I asked my class. One student proposed wars and the consequent culling of age groups. That doesn’t seem quite right. Did only 18-19 year-olds die in battle, but not the 17 or 20 year-olds? If so, did it happen repeatedly, every fewer years? Unlikely. My answer, which I think is the most sensible, is that it’s reporting error.

Two likely explanations

1) Birth records weren’t all that carefully kept or managed. Maybe people didn’t know how old they were and they just rounded. This is possible. But I never saw my birth record while growing up and I knew how old I was. People in 1850 weren’t stupid – they knew how calendars worked.

Looking again at the histogram there is another reason why this explanation doesn’t seem right. If the argument is that records were shoddy, then we would expect that older people would be rounding their age more. After all, if birth records were poor in 1820, then they were surely worse in 1790. But the graph shows the opposite – the clustering of ages largely disappears after the age of 35.  The change is dramatic. Severe rounding occurs at younger ages, then the distribution smoothly decreases during middle-old age.

2) The census survey was completed by the head of household. This was typically a dad. Children might live at home well into their twenties, depending on when they would marry. So, a dad is completing this census survey. It’s not the most important thing in his life. The survey asks how old each household member is. He looks around at his adult child and says to himself “What are you? Eh, you’re about 20 years old. And you? You’re about 15.” The histograms bears this story out. The bar widths are ~2.5 years, which means that every other bar contains a multiple of 5. 

Dads aren’t stupid. They don’t round up to 20 when they have an eleven year old. But, 18 is a lot like 20…. Or, it is when you’ve got a lot more important things to think about. Maybe my dad was just anachronistic, or old fashioned. But, now I know that fathers rounding their kids’ ages is as American as apple pie and that they’ve been doing it since Lincoln was alive.

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