How to be indie/hipster at a young age?

Well, if you mean in music, start listening to "indie" music: Grizzly Bear, Coconut Records, Best Coast, Ghost of a Saber Toothed Tiger, The Dead Weather, My Morning Jacket, etc. are good bands to start with. Same with movies "independent" and "low budget" films: Wes Anderson, Jim Jarmusch, Roman and Sofia Copola films are good places to start. For fashion, skinny jeans are pretty much a must. There are tons of branches of hipsters, but oversized on downs, and basic relazed tees are part of the "uniform". Keds, vans, converse, any kind of streamlined athletic shoe. Of course, these descriptions are just based on perception. Make sure you create your own niche, your own you. Without that, you can't be "indie"!