When do men and women reach their individual sexual peaks differently?

Everyone's different. It depends to a great extent upon what you mean by "sexual peaks". When you look at large groups of men & women, it's been said that men tend to engage in sex frequently in their teens to 20s while women tend to increase sexual frequency in their 30s to 50s. However, this isn't as important as the individual's sexual habits and finding an appropriate partner to match.