Although some of these costs will be the same for males and females (risk of STIs and impairing long term mate value), the costs for women will be more severe due to paternity uncertainty (cues of multiple mates will be disfavoured by males).preferences for age differences were measured and research supported the theory that people prefer to marry close to the age when female fertility is at its highest (24–25 years).In all 37 cultures it was found that males preferred females younger than themselves and females preferred males older than themselves.
This theory predicts both intrasexual selection and intersexual choice due to differences in parental investment; typically there is competition among members of the lower investing sex (generally males) over the parental investment of the higher investing sex (generally females) who will be more selective in their mate choice.
However, human males tend to have more parental investment compared to mammal males (although females still tend to have more parental investment).
age disparity have developed over time and vary among societies.
Differences in age preferences for mates can stem from evolutionary mating strategies and age preferences in sexual partners may vary cross culturally.
Parental Investment Theory refers to the value that is placed on a potential mate based on reproductive potential and reproductive investment.
The theory predicts that preferred mate choices have evolved to focus on reproductive potential and reproductive investment of members of the opposite sex.
Analysing the results further we see that cross culturally; the average age females prefer to marry is 25.4 years old, and they prefer a mate 3.4 years older than themselves, therefore their preferred mate would be aged 28.8 years of age.
Males however prefer to marry when they are 27.5 years old, and a female to be 2.7 years younger than themselves, yielding their preferred mate to be 24.8 years old.
There are also alternative social theories for age differences in relationships as well as suggested reasons for 'alternative' age-hypogamous relationships.