There is considerable evidence that testosterone actually DECREASES male lifespan, perhaps by as much as 20 years. For example, from a very well controlled study on the lifespans of Korean eunichs:
http://www.sciencedirect.com/s...:
"The average lifespan of eunuchs was 70.0 ± 1.76 years, which was 14.4–19.1 years longer than the lifespan of non-castrated men of similar socio-economic status. Our study supports the idea that male sex hormones decrease the lifespan of men."
I entirely support having the choice to take testosterone, for whatever reason one would like. I have a friend who's life has been quite improved by testosterone treatment, in fact. BUT taking T to help with unspecific effects of aging is a dangerous experiment and fad and people should be aware that there are likely to be some very serious and unforeseen consequences. I managed to talk my aging father out of this treatment, and as a consequence I just may be able to enjoy his company for years to come. Any doctor who suggests taking T to prolong lifespan is either critically misinformed or displaying severe lack of judgement, imo. And the author of that paper, who keeps referring to T as a magic wand? He is an idiot.
I'm not a medical doctor but I am a PhD and I have done studies on the effects of sex hormones on animals. It's not clear why testosterone might decrease the lifespan of men, but one likely candidate is the fact that testosterone clearly decreases immune system function.