I'm not in the habit of taking cold showers, but I noticed a significant difference in libido after swimming in a friend's cold pool this summer, for a weekend.
The effect wasn't placebo, as I wasn't expecting any effect. I was just swimming. It just happened, and i felt much better for a few days. So, as far as it being "bro" science, I'll say that I believe that a lot of doctors are too arrogant in their knowledge of the body. Show me a doctor who can cure himself of a low libido, naturally, and then I'll listen. Until then, discounting the experience of a group of people, who have conducted an experiment that you have not, isn't valid. Unless your a specialist in adaptive medicine (high altitude training and the like).
I'll try out the cold shower routine and report back. However, I'm not a Latino, and so maybe I won't benefit from the super-Latino-power that Moma ascribes to Mixx not aging. We'll see.
What I will say is that if the body has an adaptive response to cold water in that testosterone is increased, then its very likely that the opposite effect occurs in hot water. The body may adapt by lowering testosterone. Just a hypothesis, based on the clear logic of the statements here.
I do know that ice cold temp will create an inflammatory effect after a short time, as well, which speeds aging (an extreme example is frostbite - but sub-clinical exposure to ice cold temps could also create an inflammatory response that, while not burning the skin beyond repair, might create inflammation in your system). You will notice this response when you see that your skin becomes warm and red after you remove an ice-cube from it. Well, the same response can occur in your vascular system and your organs. Therefore, I'd shy away from bathing in ice. I would build my tolerance slowly, through room temp showers at first, and then cold showers or cold (not iced) pools/baths later. But that's just me. The pool that I swam in was cold, but not ice cold, and it had a pretty significant effect.
I think that the testosterone jump is probably a result of the body temperature decrease that comes with your heat dissipating into the water (think about it, your body naturally keeps your testicles colder than the rest of your body - at least mine does - I think that it does this to maintain testosterone production).
The second mechanism could be through creating a short term inflammation effect, that your body responds to through raising your anti-oxidant defense and testosterone. The trick would be not overdoing the cold showers or baths, temperature wise, so that you injure the body to the point where there is no "rebound response" in testosterone versus creating a short term stress that your body can readily handle, and responds to with a testosterone boost. Just a thought. I'm looking forward to trying this out. Good thread.