Hello,
Penis grows uptil puberty i.e. till 16-17 years of age. The normal length of penis is between3.1 to 5.1 inches in length.I hope that helps. Take care and regards.
Penile growt and development take place during puberty. You stop developing at about age 18 to 21. If you have not developed properly there could be something that is the cause of this.
All the best,
Ron