18 and balding or adult hairline?

[Unterleigen]

I agree with you that the idea of a mature hairline is somewhat silly. A mature hairline is a mature hairline until it's a Norwood 2.

Nevertheless, I think her point is that slight frontal recession is so common that it is not necessarily pathological and doesn't predict further hair loss. Simple observation will confirm this. How many 40 year old white males do you see with hairlines that look like those of boys or women? Probably none. Even those we describe as having a full head of hair will usually not have a totally straight hairline.