I'm not afpx, but I understood them to be saying "you have fewer good days when you're 50 than when you're 18." That is, health wise, it's better to be 18 than to be 50. :)

A related concept is the quality-adjusted life year (QALY), which is used when weighing the cost/benefits of certain interventions.

[1]: https://en.wikipedia.org/wiki/Quality-adjusted_life_year

Oh so when you’re 18 you extract as much pleasure/utility/etc from a month of life as you do from a year at 50? Maybe my late teens were lame because those times were not that awesome lol. Nor any other time I can think of. It’s all mostly been the same, except, say, when I was 4-8, when time just dragged on and on so slowly everything felt like eternity all the time. Then that ended and everything has been more or less the same from a psycho-emotional perspective.

Health-wise yeah it’s great to be young :)