So, how does one ensure that testosterone levels remain in balance? Some doctors suggest that monitoring testosterone levels every five years, starting at age 35, is a reasonable strategy to follow. If the testosterone level falls too low or if the individual has the signs and symptoms of low testosterone levels described above, testosterone therapy can be considered. However, once testosterone therapy is initiated, testosterone levels should be closely monitored to make sure that the testosterone level does not become too high, as this may cause stress on the individual, and high testosterone levels may result in some of the negative problems (described previously) seen.
Total testosterone goes down by about 1-2% per year , starting sometime in your 30s, and bioavailable testosterone decreases by about 2-3% a year. Those numbers can be pretty misleading though. Men approaching middle age tend to exercise a lot less, and eat a lot worse. So nobody really knows what a “natural” decline in testosterone looks like, on a population-wide basis. It’s kind of like saying muscle mass decreases 1-2% a year once you hit middle age … that decrease can have a lot to do with more time spent on work and family, and less time spent trying to get ripped to attract a partner (among other reasons, of course).