By Austin Frakt

American life spans are rising, and as they are, health care spending is, too. But longevity is not contributing to the spending increase as much as you might think.

The median age in the United States will rise to about 40 by 2040, up from 37.7 today. That’s partly because the average American lives three years longer today — reaching nearly 79 years old — than in 1995. The Congressional Budget Office credits population aging for a substantial portion of its projected increase in health care spending — from 5.5 percent of the economy today to almost 9 percent by 2046.

But research suggests that living longer, by itself, isn’t a big driver of rising health care spending. Because the baby boom generation is so large — members of which are now in their 50s to late 60s — the average age of Americans would…