Some of what you mention is biological, but much is also attitudinal. In other words, you have some choice in how you spend your later years. In fact, I'd say

Some of what you mention is biological, but much is also attitudinal. In other words, you have some choice in how you spend your later years. In fact, I'd say that much of your range of choice then will be dictated by earlier decisions. If you choose an atypical and dynamic life in your younger years vs settling into a "standard" lifestyle, you're more likely to live out your older years with fewer constraints of the form you fear.