Does androgenic alopecia affect 18-year old males. Both father and mother have very low hair density. (Photos)

Androgenic  alopecia can begin in the teens. You should visit a hair loss expert who will do a good examination  with magnification and history. If your scalp has decreased density and hair shifts that differ in size as well as miniaturized shafts you may have androgenic alopecia.
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Yes, androgenetic alopecia can affect 3-5 % of individuals under 20. There are many mimickers or lookalike conditions so it’s important to edamine the area up close. Early on it can be challenging to differentiate androgenetic hair loss from other conditions. However, a carefully obtained history, detailed scalp examination including dermoscopy can usually distinguish them. The vertical lines (known as logitudinal melanocychia) usually has no connection to hair loss. A dermatologist can advise you on these lines and may examine other areas of the body as well (includingthe mouth) for similar pigmented areas.

Your biggest enemy is the progressive thinning leading to a balding pattern that may not evident at this point in time. The degree of thinning that you are experiencing 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 may be presently having. If the diagnosis is early genetic hair loss (the most common cause of hair loss in young men and you are probably following your families balding problem), 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 best test to get is the HAIRCHECK instrument test which will determine the Bulk Measurements of your hair and this will show, over a one-year time frame, how effective the treatment will be or if you are not on drugs, using this instrument to tell you if you have ANY hair loss at all.  Once you know this information, then you and your doctor need to develop a MASTER PLAN which will define what you need