Some boys may still have a growing penis at age 18. Male penile maturity is usually between the ages of 18-20 years old, depending on the physical and developmental status of different people, generally after the age of 18 years old penis are still have some room to grow. A normal man’s penis is beginning to mature at age 18, and some men’s penises will stop growing. Some men, in the 18-20 years of age period, such as can maintain a good physical and mental health, appropriate to strengthen the nutritional intake and carry out certain targeted exercise, strengthen the penis hygiene cleaning, the penis in the 20 years of age before there may still be a certain growth. Normal adult male penis erect state, as long as the length of 9cm, generally belong to the normal. There is no clinical treatment for a small penis. In summary, if there is a problem with genital development, you should seek medical attention.