Gynecomastia in a Teenager (Endocrinology)

Medical Case Details:

A 13 years and 9 months old overweight male, 65 kg and 152 cm tall. Non-consanguineous marriage. FT, AGA(3.7KG)LSCS to G1P1A0 IDM baby with the good Apgar score. Normal development history, normal IQ, no dysmorphic feature. He was fed formula milk (PediaSure) for all most 2 yrs. Initial childhood, he was slim, and he started to gain weight after 7 yrs of age. This patient is steadily increasing his weight and has developed profound B/L gynecomastia. Fat deposition on his tummy and his voice is not yet changed and has a normal penis but a little smaller in size. Testis are of normal volume. The father's height is 158 cm, mother's height is 155 cm. Parents attended puberty normally. CNS and Fundus exam normal. No crossing of centiles. Baseline: All routine investigation has done as follows: Insulin (did on 15.01.2018) - 85 increased (normally less than 25). 29.10.2018 - 45 increased. Free T3 (done thrice) - increased. Creatine - decreased. ALT - decreased.

What can be the probable diagnosis of his gynecomastia? Please suggest proper treatment and management. I am worried about his gynecomastia. He is a decent, well-behaved, and intelligent child, but with a sedentary lifestyle. Please help this child to reach a diagnosis.