Hopefully, you’re going to die a very long time from now, surrounded by friends and family, having lived a meaningful life.

But exactly how far away is death going to be? When you look at the broad sweep of human history, life expectancy has pushed upwards(albeit not always in a straight line), almost doubling over the last century. And it may well keep rising. Andrew Scott, co-author of The 100-Year Life: Living and Working in an Age of Longevity, believes that longer lifespans are about to alter society in some fundamental ways.

“The trend over the last 200 years, is that every ten years, life expectancy has increased by two or three years,” Scott said. “So what that roughly means, is that you’ve got a good chance of living six to nine years longer than your parents ... [so] children born in the rich countries since 2000 have got a more than 50 percent chance of living to 100.”

That, to put it mildly, is a long time.

And, according to Scott, society is designed for people to live, on average, about 70 years. That’s how Social Security and retirement are set-up. We expect people to go from childhood, to working adulthood, to retirement. With a longer average lifespan, we’ll have to rethink some of those milestones and life stages.

In fact, longer life expectancy (along with other societal changes) in the 20th century led to the creation of two entirely new stages of life: the teenage years and retirement. That’s right: there were no teenagers in the Middle Ages. At least not teenagers as we would think of them.

“For most of human history, you just had children, and then you became an adult,” Scott said. “But, as we lived for longer, as schooling was extended, we had this intermediate stage of adolescence.”

And, just like the rise of teenagers in the 20th century, our increased lifespan in the 21st century is going to lead to major changes. Scott says that we can already see some of them right now: “People are getting married later, buying cars, buying houses, having children later.”

According to the Pew Research Center, 20 percent of adults from 18 to 29 are married, compared with nearly 60 percent in 1960. Scott suggests that we might want to think of another new life stage, this time between being a teenager and a young adult.

The implications of all of this can seem a bit frightening at times, even if you just look at something like retirement. Increased lifespans could even be unequal, with the rich living longer and the poor not keeping up.

But Scott points out that overall, increased longevity is a good thing, both for society and for the individual.