There isn’t a specific time where a woman would be more into sex. It can start right from the moment the girl hits puberty. 14yrs is a good age, or even 18yrs, the age where girls want to be seen as potential women, that is the age when they probably will be knowing about their bodes as well as sex, so I think using any word other than desperate for sex is an understatement.
As you opine the interest doesn’t come with age, it crops up with lack of sex. For instance women in their early and late twenties don’t look over horny on the outside because they get their regular share with either their boyfriends or their husbands. Often the guy would be thinking, “she acts so decent when she is out, but she acts like a real bitch with me”; so when they are getting what they want they don’t really desire it like the ones that don’t get any.
Men or young boys often think mature women ranging from 38-45 or even 50yrs are more desperate since they don’t get sex regularly with their partners loosing interest in them, but if they are active in sex, even this age isn’t the high desirous age.
So the answer to your question, there is nothing called the age where women long for sex the most. Women realize their sexuality at different ages and hence they act desperate with it, its completely personal and it isn’t general.