Should I start using Finasteride at 20-years old? (Photos)

Yes, you can use finasteride, but it may have side effects. I suggest a consultation with a cosmetic dermatologist with experience in hair restoration and maintenance. Some great options for hair restoration and maintenance are prp injections which can stimulate hair growth. Hope this helps.

Thank you for your question. I suggest that you move forward and consult with a board certified facial plastic surgeon to develop a hair regrowth treatment plan. It may include finasteride depending on your candidacy, and how the medication fits with the other strategies.
Best wishes,

This needs an in-person evaluation. I suggest seeing a hair loss expert now to evaluate and go over your condition and provide you information about your best treatment options. There are great non-invasive options like prp/progesterone and/or hair transplantation. 
See an expert. Best, Dr. Emer

Whilst you are right in being cautious about side effects with finasteride it is important you weigh up the benefit of hair loss vs the side effect risk of taking the medication. If after starting the medication you start to suffer from its side effects be aware that there are plenty of other treatment options out there (Minoxidil, PRP, Hair transplantation etc.) 

I am pleased that you are going to see a doctor. The drug finasteride has side effects, but they are low. Despite this, you must be fully aware of these side effects.