I don't know why everyone assumes just because you have a very high forehead or a higher hairline, that you are more likely to lose hair. Sensitivity to dht causes hair to stop grow, not where your hairline begins. It's a matter of scull shape etc.
Yeah you might maintain the Norwood 2-3 "mature" look for a long time OR you might go NW6-7 in a couple of years. Don't take your chances. I also deluded myself for a while into think it was just a mature hairline and now I wish I had researched finasteride and Rogaine earlier.