Age disparity in sexual relationships

Significant age disparity in sexual relationships has been and remains a feature of couples in many cultures and societies. Historically the most common pattern in heterosexual couples is an older man with a younger woman ; although the average age gap between men and women at marriage has been narrowing as women have gained greater financial independence. This may be brought about as an arranged marriage, or either member may pursue and initiate this relationship. Homosexual relationships of both sexes may also exhibit age disparity; when between an adult male and adolescent boy, the term "pederasty" is sometimes used, especially in European historical context. In extreme cases, age disparity may be seen as dysfunctional (a paraphilia) if such relationships are pursued to the exclusion of all others and to the detriment of the partners. Sexual relationships involving an adult or adolescent and a prepubescent child are defined as child sexual abuse in most societies.

Motives
Factors leading into a search for a significantly younger or older individual with whom to share an intimate relationship can vary wildly. A common perception is that younger mates serve the purpose of a "trophy" or object of status, while older mates are perceived to have greater resources, wisdom, or sexual knowledge.

Many psychologists study the phenomenon of age disparity, and have observed certain extremes of this behavior.


 * Chronophilia is a general term, applied to any age-related preference that is outside their own age group.
 * Ephebophilia is the attraction of older individuals to adolescents.
 * Hebophilia is the attraction of older individuals to pubescent youths.
 * Pedophilia is the attraction of older individuals to pre-adolescents.
 * Infantophilia is the attraction of older individuals to small children (ages ranging from 0 to 5).
 * Gerontophilia is the attraction of non-elderly individuals to the elderly.

Age disparity as an indicator of paraphilia
There is also the issue of whether age-disparate relationships are a significant indicator of paraphilia. Individuals who exclusively pursue age-disparate relationships may be classified by psychologists as parasexual, that is, their behavior is qualitatively different from the norm. Individuals who occasionally pursue age-disparate relationships are not included in this category, except in the popular press.

The "half-your-age-plus-seven" rule
The "half-your-age-plus-seven rule" is a rule of thumb in Western cultures defining a mathematical formula to judge whether the age difference in an intimate relationship is socially acceptable. Mathematically speaking, the rule is:


 * $${\text{Age of Younger Individual} \ge \cfrac{\text{Age of Older Individual}}{2} + 7 \text{ years}}.$$