re:
I think this is a very good decision made by you and your doctor. There is little evidence that 1 mg finasteride can negatively effect an 18 year old, but there is clearly not enough research on the subject. Therefor, if there are any potential negative effects, then it is reasonable to conclude that at a reduced dosage of 0.25 mg, there is even lower risk.Once you hit 21, you can upgrade to 1 mg per day.
I would make sure to pay attention to your body and the best thing to do is start a daily diary writing down how you feel.
As far as the minoxidil, I strongly suggest waiting for six months so you can evaluate the effects of the finasteride. Let's say you start minoxidil and finasteride use today. In four months, when you have some regrowth, you will have no idea whether it was the finasteride, the minoxidil or both. For all you know, finasteride could do nothing for you and it was actually the minoxidil. Also, minoxidil may cause side effects and you may confuse minoxidil sides with finasteride sides. Remember male pattern baldness is progressive and a few months will not kill your hair. My only regret is that I started finasteride and minoxidil use in the same week.
I think once daily application is your best bet at your age.
