20 years old and I have noticed my hair thinning on my hairline. Am I going bald? I can see the skin clearly on my head. (Photo)

Posting photos of yourself cannot determine you if you are going bald, especially if there are no BEFORE photos.  If you believe you are going bald see a doctor for a proper exam.

This is likely early AGA (androgenetic alopecia). Be sure to see a physician to specializes in hair loss for guidance. In general treatments for genetic hair loss include1. FDA approved treatments such as minoxidil and finasteride2. other treatments such as low level laser and platelet rich plasma3. natural treatments such as rosemary oil, pumpkin seed oil4. shampoos containing zinc pyrithione or ketoconazoleOption 1 is by far the best with finasteride being a superior treatment compared to minoxidil

Your biggest enemy is the progressive thinning
leading to a balding pattern that is not evident at this point in time. The
degree of thinning that you think that you are showing would suggest that you should see a
doctor who most likely will get Bulk Measurements of your hair to determine the
degree of the thinning that you are presently having. This test is an accurate way to diagnose very early balding. If the diagnosis is early
genetic hair loss, then the best treatment would be the drug finasteride which
is highly effective in men of your age and may not only stop the hair loss but
possibly reverse it. If you are developing a more advanced balding pattern the
the best test to get will determine the Bulk Measurements of your hair and this
will show, over a one year time frame, how effective the treatment will be.
Once you know this information, then you and your doctor need to develop a
MASTER PLAN which will define what you need to do over the years to come.

it seems to be some miniaturization and early stage of androgenic alopecia. It is a good idea to see a hair transplant specialist and start on a medical regiment.