i would say NW2.5, though it does look a bit too far receeded to be a mature hairline.
most people recede from a NW1 to a NW2 in their early 20's or late teens, it is called the mature hairline.
but in your case it looks like it has gone a bit further... are your family members BALD?
i would maybe wait a few months and then see if it gets any worse, then get on finasteride. (actually if it was me i'd be on finasteride straight away)
finasteride should maintain what you have, maybe try minoxidil if your scalp diffuses (temple hair seems notoriously hard to regrow though)
if you are a responder to finasteride you might keep that hair for years and have decent hair for decades