Chronophilia refers to a fetish in which one is sexually aroused by the idea of age discrepancy between the sexual partners – young women being turned on by old men, older women being aroused by younger men…etc.
It actually has ties with multiple paraphilias (graeophilia, teleiophilia…etc.) and has to do with the person’s sexuoerotic age being discordant with his or her actual chronological age and is concordant with the age of the partner. Meaning that the person with this disorder is identifying with someone who is either much older or much younger than himself or herself and thus mimicking the other.
Chronophilia could be used to describe something minor like 40-year-old cougars being attracted to 20-year-old men, to something far more serious and horrible like pedophiles.