The correct answer to this open question is the following.
The lifestyle I think is the healthiest for aging people is the activity theory.
This activity theory has more pros than cons. For instance, the disengagement theory establishes that it is ok to age and withdraw from society to spend time only with people of the same age. But this diminishes their vitality, in comparison to spending time with young people or other groups. The continuity theory establishes that people continue with their same thoughts, believe systems, and personality traits until they die.
However, the activity theory says that people can stay active physically and mentally, and learn new things or change, which results in more willing to live and stay happy.
My examples are musicians, for instance. You just have to see old rockers such as Mick Jagger or Keith Richards that both still rocking on stage like in the 1970s. They move, they play, they enjoy, and they show too much life.