What is the normal range of free testosterone in nmol/l for a 20 y/o male?

Why do you ask?: You can find reference ranges here. https://www.healthcare.uiowa.edu/path_handbook/handbook/test1802.html Worth remembering. If you used to get great erections and were horny most of the time, and it's largely stopped, you don't have XXY or primary hypogonadism. Losing libido at your age is often due to prolactinoma and/or hemochromatosis with normal testosterone levels.