It will be interesting to see what results life extension provides us this century. I have thought about this topic and the idea of being 100 years old with all my friends dead is quite haunting. However, though your older relatives would be dead you would still have family around in the form of nieces, nephews (kids, grandkids perhaps even) and so on so it's not like you'd have no family around. If life extension means you can be a 100 but have the body of a 60 or even 70 year old then I'd be up for it.