Especially to do things by around the age of 30. According to society you should be having lots of fun/travelling/dating in your 20s, then when you reach about 30 you should be settling down with and marrying one person, with your first child appearing a year or so after the wedding.
As a female you should be dating a male at least the same age or ideally 3-4 years older, and who earns more. God forbid a woman would date a younger man.
Just starting to think this is the expectation of people in society, and that it's incredible how many people follow this pretty much to the letter.