Hair THINNING can be caused by both aging and androgenic factors. If your hair diameter just gets smaller from turning gray but still completely goes through all the normal hair cycles throughout your life, you will still have the same amount of hair. However it might look thinner because of the gray hair and contrast to the scalp.
On the other hand, with androgenic hair loss, your hair no longer goes through the normal hair cycles and eventually the hair because vellus or not visible anymore so you really notice loss and we call that balding or bald. Obviously men who never go gray until much later in life like 70's are going to have NW1s as long as they don't they don't have the gene to go bald.
One of two men by the age of fifty is going to show some hair loss and I am really now believing it is mostly do to androgenic cause instead of aging. I used to think it was aging but I no longer do. Diffuse thinning without any Norwood pattern is a little more confusing since it still tends to be a full head of hair but just less density. But in most cases, its the hair line that most people focus on and that area is the hardest to treat. If you look at most threads, its all about the hairline. And that is understandable as it frames your face. And I still believe, the "mature hairline" is still the very first stage of androgenic alopecia. Any person that keeps their NW1 throughout their life does not carry the gene for androgenic alopecia.