It is a matter of heredity, if you look a little you will see that the penis of Africans or Nigerians is much bigger In our country, on the other hand, the penis of a man is a little smaller , depending on the weather , environment and race. 5.9 inch penis but much larger. Since you are 13 years old, you are more likely to grow up. The body grows by 20-21 years so the penis will also get bigger.