The sexpiration date is the stage when women's looks starts to fade. The stage whereby women reach their sexpiration date is earlier than men. Thats mainly because women have a shorter fertility period and also because men can supplement their appeal via status, whereas women can't as much. Because of this contrasting window of opportunity, female beauty is sometimes compared to milk, in reference to the expiry date.
To become milkmired means that you have aged like milk (i.e. became expired rather quickly), in contrast to someone who ages like wine. It is a portmanteau of milk and expired. Sometimes the term "sexually expired" is used. Milkmirers often face the unfortunate side-effect of not being able to date people their own age: only older. A denarian (teen) milkmirer looks like a vicenarian. A vicenarian milkmirer looks like a tricenarian. As such, young milkmirers are indirectly forced to interact with milfs, cougars, manthers, sugar mommas and cradle robbers whether that is their niche or not.