I grew up in NYC and just completely disagree with your analysis here. There are a lot of hidden costs to live in NYC such as some of the highest income and sales taxes in the country, apartments where even if you own if a problem is found the forced maintenace costs can go up thousands a month and you get evicted for not being able to pay. Health driven by sin taxes on soda and tobacco, and much more along those lines than just people walking places.

It is true that older people in NYC are seemingly healthy, but they're definitely a very specific type of person.