Like everything in nature, your penis goes through a series of changes over your lifetime. Each phase is controlled mostly by your testosterone levels.

Somewhere between the ages of 9 and 15, your pituitary gland releases hormones that tell your body to start making testosterone. Puberty begins and brings changes. Your testes (testicles), scrotum, penis, and pubic hair all begin to grow. Testosterone levels peak in your late teens to early 20s.

The amount of testosterone in your body may drop slightly in your late 20s through your 40s, but the change is minimal.

After 40, your total levels may drop only a small amount. But your body slowly begins to make more of a protein called sex hormone binding globulin (SHBG). This sticks to the testosterone in your blood and lowers the amount your body has available to use.

As testosterone levels fall, you'll notice other changes to your You may notice that it doesn't seem as large as it used to. The actual size probably hasn't changed at all. But if you have more fat on the pubic bone just above your penis, that area can sag and make it look smaller.

As testosterone levels drop, erectile dysfunction becomes more likely. You may lose rigidity, but not necessarily your ability to have intercourse.

Perhaps the most common culprit is the body's inability to hold blood in the penis. When this happens, you may be able to get an erection but not keep it. Blood flows in, but the aging muscle that surrounds your erectile tissue can't hold it there. The result: lost hardness. In this case, Viagra will help.
Viagra will make a man's penis harder, and some men may experience Penis Growth and ED when taking Viagra. But Viagra will only increase blood flow to the penis.