I think a "mature" hairline can be considered mild male pattern baldness although I don't believe it means a person will necessarily become bald. For example, take a look at some well known celebrities such as Charlie Sheen. He obviously does not have the same hairline now as he did in "Platoon" 20 years ago, but the rest of his hair is thick, and I personally don't consider him to be balding..his hairline pretty much has remained the same in his 30's and now into his 40's. Maybe he had some work done...who knows, but the point I am making is that it is very natural for a guys hairline to recede somewhat as he gets older, but can stabilize and stay where it is and he could go to his grave at 75 with the same head of hair he had when he was 35.