Gynecomastia is common in the newborn and it usually resolves within the first year of life.
Again in puberty, gynecomastia is common. How common is the subject of debate. The most acceptable figure in my mind is a frequency of about 65% or 2/3 of all boys. Again it is common for it to resolve. There are again lots of different opinions as to how good the odds are of self resolution; Which is why surgery is usually not recommended until it can be established that the young man is through puberty.
Late in life, when age causes a slowdown in Testosterone, Gynecomastia is again common though this time it is not even remotely likely that it will resolve.
Of Elderly men in nursing homes, the number of men with Gynecomastia again rises to about 2/3 of all men.
The percentages of self resolution in infancy would seem to be near 100%.. In old age, near nil..
The number of young men who have self resolution in or after puberty is questionable. Reliable information must exist somewhere, but most of the information I have seen has some degree of bias built in. I have seen the numbers estimated as high as 90% having self resolution, Which I disregard completely. I've also seen a report that said more than half of the boys with Gynecomastia would have it self resolve; This may be believeable.
It runs in my family, This is not uncommon. The men have well contoured (though small) feminine breasts and the women of the family all have very large breasts.
Your most important tool is information. Talk to your Dad, If he had it but it went away; You might expect the same thing. If your mother has a brother, find out what his history can reveal. Ditto with your grandparents.
You are not in the least odd, This condition is more normal than many people think.
Keep a good attitude and hope your parents provided you with all the right genes.