I should also note: that my maternal grandfather shared a very similar hairline to me; he had a very distinct "V" shaped hairline, with his left side going more inward than the right, thus creating a natural "part". As he got older, it progressively matured to a 2.5 in his mid-40s, and then a NW3 in his early 60s and remained this way. He also retained this distinct "V" shape.

Anecdotally, no other person on either side of my family seemed to share the same hairline shape as me, other than my maternal grandfather. My twin brother has a slight widows peak and very slight recession in the front, but other than that, the hairline seems to be straight across (like my father had as a kid).