(Pictures) Do I suffer from Retrograde Alopecia ? (20 years old male)

A formal diagnosis with a hair loss surgeon is highly advised. Given your relatively young age, waiting to see how your hairline and hair density changes in the next few years will grant you a better understanding of the effectiveness of different hair restoration treatments, be they surgical or otherwise. 
If the diagnosis is early genetic hair loss, then the best treatment may be the drug finasteride which is highly effective in men of your age. It may not only stop the hair loss but possibly reverse it.
For early prevention I may recommend starting with over-the-counter minoxidil treatments (Rogaine) mixed with GroMD’s shampoo and follicle activator spray.

Thank you for your question, 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

It’s impossible to tell from a photo. You’ll need to examined by a hair specialist to see if you are actually thinning.  And other causes will need to be ruled out. 

You need to be examined by a doctor who specializes in hair diseases and hair loss.  This requires an expert examination and a series of blood tests along with a complete history of medications you might be taking