Morning wood, also called nighttime penile tumescence, is a normal physiological process in which men get erections while they sleep, usually when they wake up in the morning. While you sleep, your body goes through normal biochemical processes that cause this. It has nothing to do with sexual desire. If you want to hear morning wood the most, you should be a teenager or young adult, when your testosterone levels are high. But for many men, it can last into their later years, though hormonal changes and other factors may make it less regular or strong as they age. There is no set age when morning wood stops for everyone; it's different for each person. Some men may still feel it well into their senior years, while others may notice it getting better sooner.