That's an interesting theory, and not unreasonable. Research does show that retirees tend to reduce their spending by about 1%/year, so after a decade and a half, that's almost 15% net reduction, after accounting for higher medical bills.

I can easily imagine that as you reach advanced age, in most cases, you have fewer friends (as others pass away), you're less likely to feel up for travel and adventure, and have less patience for many things.

Of course, there will be exceptions. Some people seem to just never slow down... 🙂