Differences in genetic relatedness between parents and offspring result in the ideal spouse not being the ideal in-law and the ideal in-law not being the ideal spouse. As a consequence, parents strive to control the mate choices of their children and get an in-law who complies with their own standards, whereas their children strive to escape from this control and get a spouse who is more compatible with their own preferences. On this basis, the hypothesis is tested that in order to control the mate choices of their children parents prefer them to marry earlier than their children themselves prefer. A second hypothesis is tested that parents prefer their daughters to marry earlier than their sons. In addition, as older mates are more costly to children as spouses than to their parents as in-laws, the hypothesis is tested that parents prefer their children to marry older individuals than their children themselves prefer. Finally, it is hypothesised that parents would like the age difference between their sons-in-law and their daughters to be greater than the age difference between their daughters-in-law and their sons. Evidence from two independent studies provides support for all four hypotheses.