I agree with the thoughts of Gulshan ji and Pradeep ji and I like the comment of Gulshan ji that a hundred year old man would be just middle aged....To add to this he might be seen roaming around with girlfriends, going to the gym and discos and might be the strongest person at that age!!! :P :P
So lets be contented with the present life span as increasing of life span will surely lead us to problems which has been very beautifully pointed out by the honorable members of our site...