This could possibly be a huge untapped seam in the book market. The idea is to describe what most people regard as having fun on the road to happiness. This is not a self-help book, or targeted in any way. In fact when you buy one of those books you are reading about distinctly unaverage viewpoints.
This
book describes the fattest part of the bell curve for every age, a statistically common perspective on having fun.
I'd imagine this book could well help people put their own lives in perspective as well as many similar books with different themes e.g. "The average way a child is raised", "Common perspectives on work" etc.
Each chapter would not be a single description, but go on to describe the upper and lower quartiles etc. An online version could also be quite educational providing the average and then subsequently refining the descriptions as you input more details about yourself.
Ageing programmers like -
Drinking.
Boring juniors about how simplistic things were 2 decades ago.
Falling face-first into a technology that isn't pure marketting.
Ageing programmers might also like -
Buying a Ferrari
Starting a new life after visiting an S&M dungeon and falling in love with a 22 year-old dominatrix at the cost of an expensive divorce.
Building steam trains.
Star Trek Cross-dressing.
Re-training as an electrician and starting a collection on the side to take care of that OCD.
Maybe its just me, but when pubs ban drinking as well, I'll be in need of readjusting my norms.