A new evolutionary psychology paper says that men and women have different age preferences regarding sexual partners - but it's primarily women realize their preferences. 

Why? They believe it is because when it comes to mating, women control the market and so are biologically more selective than men. Thus, men are more likely to have sex with less than ideal partners. Women can be with the one they love, men have to love than one they are with.

The psychologists at Åbo Akademi University in Turku, Finland gathered observations from a population-based sample of more than 12,000 Finns and found that women, on average, are interested in same-aged to somewhat older men than themselves and that this pattern displays itself across the entire life-span. Men, on the other hand, show a tendency to be sexually interested in women in their mid-twenties.

This tendency is also notable when the men themselves are younger or older than this. Men younger than 20 prefer women older than themselves, while men older than 30 prefer women younger than themselves. The reason for why men's sexual interest seems directed towards women in their mid-20s is likely because women of this age are the most fertile.

This means that in our evolutionary past, men who have had sex with women in their mid-20s have had more offspring than other men. This study shows that in terms of sexuality evolution has favored differences in female and male psychology.

The study only looked at heterosexual preferences and heterosexual activity. To follow this up the researchers plan to study the corresponding pattern in non-heterosexual individuals.