It looks like there's a lot of causes, but yeah obesity is a big one for post pubescent pre geriatric gynecomastia. Apparently most boys get temporary gynecomastia mid puberty though.

Like I'm all for trying to deal with the endocrine issues the youth are currently facing. It's just that I get the strong feeling they're going to be far more interested in things like banning birth control and estrogen replacement than things like estrogen destructive enzymes in wastewater treatment (which would also stop us from changing frogs' sexes too much) or reducing dairy consumption. It's clear Kennedy doesn't care about science when it goes against his gut instinct.