6 Best Testosterone Boosters For Males Over 40 By Storyhub Testosterone is the sex hormone that promotes masculine characteristics such as muscle mass, assertiveness, and high libido. However, testosterone production peaks pretty soon after men reach adulthood, as early as age 18 or 19. Afterward, testosterone levels gradually drop for the rest of your life. By the age of 40, low testosterone levels have likely caused a variety of undesirable symptoms including low energy, increased belly fat, and a lower sex drive. Luckily, there are testosterone boosters available that can increase testosterone production naturally. However, not all natural testosterone boosters are created equal and some don’t even work at all.