20 year old black male never noticed anything till a month back. (Photos)

Hair loss has 3 main causes for males. Genetic, Stress related and hormonal. First figure out the reason causing your balding, and get the right treatment according to your problem. 

In  my opinion you need to be examined by a hair loss expert. They will do a good history, physical examination with magnification, and possibly blood work and biopsy. There are a number of diagnosis that could describe your condition. It is possible the dreads caused a traction alopecia. You may be developing a genetic androgenic alopecia.. You could have an unusual scarring Alopecia seen in African American individuals. Your hair loss expert needs to make a definitive diagnosis and develop a treatment plan.PRP hair MD.com

I'd recommend switching to organic products for your shampoo and conditioner, and to look in to preventative medications like Finasteride and Minoxidil which has been proven to halt and even reverse hair loss.  PRP would also be an option for you. Before starting any medications it is best to check with your physician.

It's an interesting scenario you've shared and likely there are a few things going on. Now is the time to get the right diagnoses and to do something to address each of these causes. There is likely some degree of traction alopecia and aome degree of androgenetic alopecia too. A scarring alopecia is not out of the question either so be sure to see an expert for proper advice.

an examination by hair loss specialist should be done.  You may have component of traction alopecia due to the dreadlocks, and/or there may be component of telethon effluvium with recent high stree, or even male pattern hair loss given location is at the crown.  A full history and examination needs to be done, in order to determine best treatment approach.  Good luck!

Sometimes the balding process starts in the crown as is shown in your picture. See a doctor and consider medications that can reverse this