The main reason not everybody is on TRT, is that not everybody needs it, or knows about it, or has some other reasons to avoid it. There is no exact age for starting the TRT – it is decided based on your testosterone levels, and how you feel. Everybody is different in that regard. I knew guys who according to symptoms and blood work needed TRT at their early 30's, whilst other guys would have above natural testosterone levels at 60. It is very individual.