I think, by that age, the pressure to settle down in a relationship and eventually a family is very much due to social expectation. Peer pressure by proxy, because many people around you, including your friends of similar ages, have probably settled down and/or become parents and it makes you feel like you have to follow suit. I've experienced similar pressure never really acknowledged it as something I wanted, but rather something I felt was expected of someone my age.

Consider that there are people significantly older than you who are still going through the same weird and wonderful phases and feelings of their lives, between relationships and perhaps balancing a desire to be social with a love/family life or vice versa. I don't think there's a set time or age to settle down and be happy. It sounds cliché, but it can and perhaps will happen when you least expect it.

Also as others have pointed out on here, work life gets in the way and leaves you too exhausted to be social. Just remember there's also people of all ages out there still looking for a reason to leave their lives of late nights out with mates behind. Sometimes having too much time on your hands can be a curse, it's all about striking a balance somewhere between work life and social life and it's not particularly easy. Either way, your social life is eventually prone to some kind of decline and a desire for something different, and that's the point where it should become clear what you truly want to do.

Simply put: Don't rush yourself, there's loads more time left on the clock to have your fun and figure out what you think is best for you. I'm not suggesting to NOT settle down since that's what you seem to want, but don't feel disappointed in yourself if you find it difficult to balance the want for settling down with the want for a social life. Go with what the heart wants while the option is still there, because one day that option may not be an option at all.