I started recently (I’m thirty) and have been on it for about six months with great results. The only side I felt so far is the mild ache in the testicles from time to time. However recently the ache has come back and is pretty persistent. And I might be paranoid but i read somewhere that propecia even the 1mg one can led to shrinking of the testicles.
If you are having testicular pain with finasteride, see your doctor and get examined. If the two are related and it doesn’t go away with stopping it for a few week, or using a smaller dose, then it might not be the drug for you.