It happens. Should still look for other causes, e.g. Steroids used for bodybuilding , other pharmaceutical drugs and marijuana. Could also be a feature of obesity. Interestingly, certain increasing prevalent environmental pollutants, for example, bpa's, can function like female hormone in the human body.
Common. Roughly half of males go through transient nipple enlargement on one or both sides at the onset of puberty.Most resolve within 6m to a year, it is considered normal.A few will have persistent or dramatic gynecomastia. It can erode someones self concept , surgery is helpful for those who don't clear up after a couple of years.