This was my first post on the juvenile hairline:  https://baldingblog.com/2007/01/12/maturization-of-a-hairline-moving-from-juvenile-to-mature-with-photos/.  This defines the juvenile hairline and from my experience, this is more genetic ‘apoptosis’ (hair death) at the juvenile hairline than the hormone interaction with the genes that impact genetic hair loss in general. I have treated many men with finasteride but have not seen the reversal of the mature hairline to a juvenile hairline on the drug finasteride.