When Does The Penis Stop Growing

Good morning doctor, I wanted to know at what age the male sexual organ stops growing. On the webI can only find discordant answers, it is not clear if at the age of 15 it has already ended, or if as some say it ends at the age of 21. fact that a person has already developed many characteristics of male development, excluding beard and perhaps bone and muscle growth, does that indicate think that penile development has already ended? (the person in question is 16 years old, he is my son, he has a normal penis…. I am asking out of curiosity, given that there are conflicting opinions). Thanks a lot.