Its not a matter of health. You can give a 65 year old the brain of a 20 year old, but you can't give him back his naive unindoctrinated view of the world. And the sheer wonderment of childhood and adolescence is something you can never recapture. I have a 1 year old. There are expressions of joy you will only ever see on the face of a 1 year old, because for them the most mundane experiences are nonetheless firsts. Similarly, you only experience anything for the first time no matter how long you live. And I think there is a tremendous creative energy arising from those firsts.

I'm partial to the idea that geniuses have one or two great ideas in them per lifetime, regardless of how long that life lasts. Given 150 years of life, I don't think Picasso would invent cubism then something else.