Why do men age more gracefully than women?

In most cases, at least from what I've seen, men are still attractive as they age, but women seem to lose a bit of their attractiveness. Of course, I'm sure it's not the case all the time, but why do you think it is? I know women are more likely to tan and get wrinkly, but men are more likely to do yard work and labor outside, so I would think both men and women get equal amounts of sun throughout their lifetimes. Is it childbirth? Make-up and hair products???