Age is actually one of those causes of low testosterone that can’t be avoided. During the puberty the level of testosterone shoots up to a very high level. That is why, a boy going through puberty starts developing body hair, deep voice, etc. But, after an age T production slowly reduces. At the age of 30, your testosterone level start reducing and it will reduce gradually till you die. That is why many men at the age between 50-80 develops “bitch tits.” Due to the estrogen to testosterone ratio in their body goes up high.