This idea seems to go back to the 1990s, though the word 'hip' to describe someone is a lot older than that and seems to have come out of the music scene in the late 1940s or even the jazz scene in the 1920s.
The word hipster started being used in the 1990s to describe urban young people, usually in their 20s, who liked independent music and films rather than following the major trends, tried to dress according to their own style rather than following fashion, and thought of themselves as politically aware but not engaged - usually vaguely left or liberal leaning, but not commiting to a party or specific actions.
There are still plenty of hipsters about, but they have attracted a lot of often humorous criticism over the years. The usual complaint is that hipsters are elitist, cynical or try too hard to seem different. However, other people admire any group of younger people who want to develop their own views and tastes.