You probably don't want to tell him your prostate is enlarged.
For one, you're only in your twenties and that would be quite uncommon for someone your age.
Number two, how could you possibly diagnose yourself as having "an enlarged prostate from hormones"?
Number three, if he had even the slightest notion that your prostate was enlarged, he's be sticking a gloved finger far up your *** to find out for himself. You'll leave his office anally invaded without a Proscar prescription.
You need to tell him it's for hair loss.