Causes of Gynecomastia

[Just4Me2Be]

What causes gynecomastia?

[Alchemist]

What causes gynecomastia?

How old are you.  That makes all the difference in the answers.

[Just4Me2Be]

What difference does age make?

[hammer]

There are times in a mans life that gynecomastia is vary normal about three times in their life during growth cycle! It with go away in most cases on its own, however, in some it stays, therefore, your age could be a factor.

[aboywithgirls]

For instance.  Mine started at puberty.  But instead of coming and going,  it came and stayed. I went through more of.a female puberty than a male puberty. Instead of growing muscles and body hair, I was growing hips and breasts. I also experienced additional, significant growth from 35-40 years old.

[steven618]

Curious as to what causes it as well. I've done quite of my own research as well as asked my GP and 2 endo's and they have told me everything from xeno/phytoestrogens over a long time, or short time depending on the body's sensitivity and it's receptors. To medication, diet, age (puberty to old age and natural low t occurance). I am about to be 29 myself and started developing about 6 months ago. Realistically about a year and a half it onset but stopped quickly but about 6 months ago i feel its really been taking off sporadically. My GP and Endo's have concluded it idiopathic. My hormones seem fine, blood tests show nothing of disease, scans show no cancers, tests show nothing else in any other organs are messed up that could cause it. They haven't checked pituitary but idk if i'd believe it was that. 
I'd definitely like to know though cause I've gone through 2 pretty good growth spurts in the last 6 months. One built a very firm wall on the side of my growing breasts under my arm and across and recently a week ago or so the projection is beginning to take place. I personally have accepted whatever happens happens cause i can't afford nor would i get surgery but it would be nice to know what is causing it.

[Paa_Paw]

There are many potential causes.  There are lists that I have found on the internet that contain over a hundred different possible causes.  Some are really odd, For example having low testosterone might be a cause, but having too much testosterone can also be a cause. 
Generally speaking, the precise cause is seldom known because the growth may have been caused by an event and the growth was not noticed until the event had passed.