He has a handsome face and everything going for him. His hairline is not one of these things. Of course it looks quite good and young, but I certainly think it could be better by being more convex. It would send a (subconscious) message "adult male", and from an evolutionary psychology point of view that would be a good thing. However, he is still young and could be 20-30 years old, so it's still not weird. If someone wants an extremely low hairline as an adult (which I'm not sure always looks good - for one thing because many have forehead muscles that would make it impossible) that also looks good 40/50 and above and not look too androgynous, then I think Brolin's hairline is just about the optimum.
This discussion reminds me of how men think that women want in men what men want in women - and women also think that men want in women what women want in men. Both are mostly wrong.