Is it typical for a 13 year old to have "1" sided gynecomastia?

Seek Consultation: One-sided presentation of gynecomastia is not unusual but it will be best for the young man to be seen in person for evaluation. The use of certain medications, drugs, organ dysfunction (kidney or liver), hormonal imbalances etc. May also be causative. Gynecomastia, if persistent, is often best treated with partial excision of the prominent glandular tissue as well as liposuction surgery.

Common issue: 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.I went through it. 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 year or so.