I was just wonder something about the frontal area when it comes to the mature hairline. You give two measurements of where the corners and the front part of the hairline should be, but what about the size of the frontal area? I think you call it the forelock? How wide can it be or does it matter?
The central portion of the frontal hairline often has a forelock of hair that can be genetically independent of the surrounding hair. David Letterman has a strong forelock that lasted longer than much of his hairline, due to this genetic independence of the frontal hairline around it. It is just one of many unique traits in our appearance.
These forelocks tend to run in families and it can be quite small or even fairly large, depending upon the genetics of the individual. Also, these forelocks often are found low on the central hairline.
We posted on a similar question about forelocks and widow’s peaks a few years back: Forelocks and Widow’s Peaks