On the aging thing I’ve just done a rough estimate. The median age increased about 3 years between 1999 and 2019, and as it’s around 40 which is before the mid-life crisis (life satisfaction being U-shaped as you age, the lowpoint around 50), an age increase of 3 years would if anything lower happiness. (Of course it would be a mix of some going down and others up depending on their ages, but the overall effect would presumably be down. Incidentally the bottom of the U-shape hasn’t noticeably got older as the population aged over this period.)
But the effect is small anyway—the median, getting 3 years older, would lose about 0.07/10 points life satisfaction (when expressed as a score out of 10), which is only about 10% of the 1999-2019 change, as well as in the wrong direction.
On the aging thing I’ve just done a rough estimate. The median age increased about 3 years between 1999 and 2019, and as it’s around 40 which is before the mid-life crisis (life satisfaction being U-shaped as you age, the lowpoint around 50), an age increase of 3 years would if anything lower happiness. (Of course it would be a mix of some going down and others up depending on their ages, but the overall effect would presumably be down. Incidentally the bottom of the U-shape hasn’t noticeably got older as the population aged over this period.)
But the effect is small anyway—the median, getting 3 years older, would lose about 0.07/10 points life satisfaction (when expressed as a score out of 10), which is only about 10% of the 1999-2019 change, as well as in the wrong direction.