your hair will get a bit thicker and will not thin as much as you age. finasteride is so harmless. just make sure you don't have prostate cancer before you start. you are supposed to get a liver check, but I don't know if liver problems are as common as testicular cancer, and i know most people don't get their testicles checked or test them themselves. so unless someone tells me liver problems are common, I'm not spending the money on a lab test. you can.
if you start finasteride young enough, it can lower your chances of getting prostate cancer. if you start older, the reduced risk of getting it is balanced by the risk of it speeding up some cancer that might develop. finasteride does not make it develop, though.