"Thirty is the new twenty" is more than just a phrase to help 29-year-olds sleep at night. There's a ring of truth to it: on average, people are getting married later, having children later, and even dying later than ever before. Hip-hop artists Dr. Dre, Jay-Z, and Macklemore have all invoked this phrase in their music (though unfortunately all of the source material is NSFW, not to mention NSFClassrooms).
But is thirty really the new twenty? The answer depends entirely on how we interpret the terminology. Developmentally, probably not; just ask any 30- year-old who has spent time with a 20-year-old.
But if you think about the phrase in terms of life expectancy, there may be some truth to it. For example, a child born in the United States today has a life expectancy of roughly 80 years. This means that a 30-year-old has cruised through roughly 3/8ths of his or her life. So one way to interpret the phrase "thirty is the new twenty" is proportionally: whereas 30 is now 3/8ths of a person's lifespan, it used to be that 20 was 3/8ths of a person's lifespan.
(Note: we're ignoring the fact that the life expectancy at age 30 is slightly more than the life expectancy at birth, by virtue of the fact that a 30-year-old has made it to 30. According to Wolfram Alpha, in the U.S. life expectancy at birth is 78.1 years, while at age 30 it's 79.69 years. However, this difference is negligible for our present purposes.)
In order for 20 to be 3/8ths of a person's lifespan, one's life expectancy must have been around 53.3 years -- more precisely, 3/8ths of 53 and a third is equal to 20. For life expectancy to have been that low, we must go back fairly far. To see exactly how far, we can plot a graph of life expectancy (y-axis) versus year of birth (x-axis). Using U.S. life expectancy data from Gapminder, the data looks something like this:
In other words, if thirty is the new twenty, we must be comparing to a twenty-year-old from around a century ago! This seems a bit extreme; typically the phrase is invoked when comparing the current generation of 20somethings to their grandparents. Then again, perhaps "thirty is the new twenty" has a better ring to it than "thirty is the new twenty-six" or "twenty-three is the new twenty," which are both valid proportional comparisons between now and 1960.
Though this proportionality argument may seem a bit academic, there does appear to be a ring of truth to it. For example, the average age at which women get married today is around 27. But if 30 is the new 20, this means that in the past, this age would have been closer to two-thirds of 27, or 18. This certainly seems like a reasonable age for women to have gotten married one hundred years ago.
But if there is some ring of truth to this line of reasoning, what does it say about the future? After all, some people believe the first person to live to 150 has already been born, and if current trends continue, it's not out of the realm of possibility to imagine that eventually life expectancy at birth will move well into the triple-digits. But if your life expectancy was 200 years, would you really wait until your late 60s to get married? It may sound crazy now, but waiting until you're 27 would probably sound a little nutty to people living in the early 1900s.
Teachers: interested in having a conversation like this with your students? Then check out our newest lesson, The New Twenty.