Thanks for query,
Secondary sexual character started to appear after 11-13 years in male known as puberty
.in it you have pubic hair.axillary hair,Mustach,Beard hair ,Your voice becomes deepened.There is nothing like growing of penis.
The growth of penis is due to its musculature & in aroused condition due to heavy blood supply it grows in size temporary.
Sex is in our mind & not in organ or penis.
Penis size has no relation with sexual satisfaction of self or partner.
So just leave all wrong thoughts about penis size & enjoy your sexual life.
You have no disease & you are OK.