Males secrete factors that block the development of female ducts and structures. Once the male embryo produces testosterone, the hormone can influence other sex-specific traits around the body. Men having nipples doesn't really have any evolutionary advantage, but it usually doesn't hurt anything either.
Barring specific medical conditions—like a tumor on ...
Evolution tends to select out traits that are harmful (in quite simple terms) AND expressed soon enough to negatively affect reproductive success. Nipples (and breast tissue) on males are extremely unlikely to have a negative effect on reproduction, which means there's no negative selective pressure on them.
Since all embryos have the tissue required to ...
Breastfeeding Management for the Clinician: Using the Evidence
According to this link 6 to 12 months healing are for a nipple piercing, but some can take as long as 18 months.
Definitely avoid it.
Chlorine and the bacteria in unchlorinated waters may both irritate
your newly pierced ears. It is therefore recommended that you wait 2-3
weeks after ...