I just joined this forum last week to ask a question about long-term hair loss treatments and older men. I expected the users here to be predominantly in their 20's and 30's (I'm 51) - that's the age you see on the Keeps commercials for a reason. So I see this thread listed in the weekly digest and I can't help but respond.
One thing I can say is as everyone grows older physical appearance is a less of a factor, for woman too. Not because people just let themselves go and don't care how they look anymore. It's because as you grow older, you get wiser. Part of getting wiser is you realize really what's "inside" is what keeps the attraction going in the long run. (Ya, I know, if your 25 and there's more guys than girls at the party, you're probably thinking that "it's what's inside that counts" saying isn't practical. But it's true to all but the most superficial women.) Now if you and your partner start eating Cheetos and Cheeseburgers 5 times a week and put on 100 pounds, it ain't going to be pretty - but that's nothing to do with hair.
Now if we're talking being attractive for the purpose of short-term relationships/encounters, I can tell you, on average, the most fun to be around and the best sex I've had 9 times out of 10 was with overweight women. For whatever reason they're less uptight, concerned about their appearance, and open minded/experimental.
I'm getting off on a tangent but my main point is, you'll learn, any women that would turn away because of your hairline or lack thereof is not a keeper. I'd worry more about your personality and how you treat people if you are concerned about being the most attractive. Just like women who get botox, stomach surgery, plastic surgery... if making yourself (in your eyes) look better, makes you feel better and act more confident, get a hair treatment or replacement surgery. But if you just think there is some bar to be met as far as hair and if you are below that bar you have no chance of being attractive, you're very wrong.