What causes "mature hairlines ?

Hello everyone, I understand that *mature hairlines" are still balding that happens to stop early and not progress to further stages but why do they happen?

Are temple hairs way more sensitive to DHT than the rest in most men? Or (like i've read in the comment that made me ask this question) do some men produce a lot more DHT while still in puberty, causing them to receed then stay there for the rest of their lives? But then this wouldn't really make sense or else we wouldn't see most people start to bald in their 30's, 40's even after testosterone levels start dropping, no?