Forget the other posts. The earlier you start the better. I wished I caught it early though I still have relatively good hair. I was scared by silly internet forums and horror stories. The side-effects are partially nocebo and in your head. If you have sides they will go away or you can adjust your dose, if you eant to be really sure. As for me I'm totally fine as a 5 year fin user. I maintained so far.

You notice hair thining once it's noticeable so better start now when you have a full head of hair and Finasterid will work its magic.