Feb 9, - Which, naturally, begs the question: Does the same happen with our dicks? “Your penis isn't made of cartilage, which means it stops growing. Apr 19, - It is difficult to know exactly when your penis will stop growing. During puberty, a young man's testicles begin to grow larger, followed by the penis. On average the penis will reach its final size about years after the testicles enlarge. Most guys are fully developed by the time they are years old.