Cross-cultural studies indicate that women's sexual attractiveness generally peaks before motherhood & declines with age. Cues of female youth are thought to be attractive because humans maintain long-term pair bonds, making reproductive value (future reproductive potential) particularly important to males

Male Chimpanzees Prefer Mating with Old Females. Martin N. Muller, Melissa Emery Thompson, Richard W. Wrangham. Current Biology, Volume 16, Issue 22, p2234–2238, November 21 2006. http://dx.doi.org/10.1016/j.cub.2006.09.042

Summary: Cross-cultural studies indicate that women's sexual attractiveness generally peaks before motherhood and declines with age [1]. Cues of female youth are thought to be attractive because humans maintain long-term pair bonds, making reproductive value (i.e. future reproductive potential) particularly important to males [2, 3]. Menopause is believed to exaggerate this preference for youth by limiting women's future fertility [1, 4]. This theory predicts that in species lacking long-term pair bonds and menopause, males should not exhibit a preference for young mates. We tested this prediction by studying male preferences in our closest living relative, the chimpanzee (Pan troglodytes). We show that despite their promiscuous mating system, chimpanzee males, like humans, prefer some females over others. However, in contrast to humans, chimpanzee males prefer older, not younger, females. These data robustly discriminate patterns of male mate choice between humans and chimpanzees. Given that the human lineage evolved from a chimpanzee-like ancestor, they indicate that male preference for youth is a derived human feature, likely adapted from a tendency to form unusually long term mating bonds

Cross-cultural studies indicate that women's sexual attractiveness generally peaks before motherhood & declines with age. Cues of female youth are thought to be attractive because humans maintain long-term pair bonds, making reproductive value (future reproductive potential) particularly important to males