Single by 30

In their senior year of high school, Peter and Joanna make a pact to go to their senior dance together if they fail to invite their desired dates. As this provides a back-up plan, this encourages them to invite a date despite the risk of being rejected. Joanna succeeds in wooing her date while Peter fails. They meet up after the dance, and they make another pact: to get married if they are both still single at the age of 30. This will encourage them to take more chances and put themselves out in the world.
(Source : Wikipedia)