There is not thing such as mature hairline. You are born with certain unique kind of hairline and if you notice it is receding ( your temples and frontal hairs are miniaturizing) you are balding. The term mature hairline is invented by hair transplant surgeons and they say that it happens to nearly all men after puberty and only 5% of men keep their juvenile hairline in order to calm down young men who notice changes in their hairline so it gets worse and they go and get a hair transplant. Believe me - MANY, MANY white men don't experience any recession of the hairline after puberty. It probably will get progressively worse trust me. Recession of the hairline is sign of greater hair loss incoming. You will either stay like this for a while and it will progress further when you get older, your testosterone level drop and your prolactin, estrogen and DHT increase or you will end up slick bald in 10 years. Some men end up Norwood 2 without vertex hairloss though. It depends on your genetics but usually that is not the case.
Fact: Perfectly straight across hairlines barely exist. Nearly everyone has a widow's peak. In some people it is just so small that it is barely noticeable.
Fact 2: You are born with unique scull structure and certain number of hair follicles with unique distribution. Your hairline should be always located on the top of your last forehead wrinkle.
Fact 3: Only sites of local hair transplant clinics write about the "mature hairline"
Fact 4:The good news is that hair loss is not permanent. The hairs just miniaturize till become so smaller and are no longer visible to the naked eye. If a bald man blocks the dht to the point when his hair follicles are not sensitive to it at all, all of his lost hair including his juvenile hairline will grow back.
As for now do not take finasteride. Tell me if you have family history of andvanced hair loss(Norwood 3 or worse) and I will tell you how to stop hair loss naturally. Hope this helps. I am waiting for you to reply again.
