We explain what's normal, at what age your…. When guys compare themselves to other guys they are usually comparing soft penises and they vary in size much more than hard penises. Hormone Will my penis still grow may be helpful for some children with this condition. A study found that the average rate of penis growth is less than half an inch per year from ages 11 to 15, after which the growth rate continues, but at a slower rate until the age of 19 or so. You should also know that even having a big penis doesn't guarantee that your partner will enjoy having sex with you. After this change in scrotum size begins, Will my penis still grow penis will begin to grow.