I'm sure if you pop down to Forest Hill on a Friday or Saturday night and visit The Hob (pub and comedy club), Sylvan Post, or the Honor Oak you'll find plenty of people in their 20s (and Question Bar, Canvas and Cream, and other places).

But it also only takes 6 minutes by train to reach New Cross, where Goldsmiths College attracts lots more people in their early 20s. And it is really easy to get to Shoreditch where I'm told all the hipsters hang out. However, I'm too old to know what a hipster is.