How long does it take to become a California state resident?

i just moved to San Fran. from New York. I grew up here and i know i want to stay here. I haven't lived here in about 8 years. I want to move back. I now live here b/c i go to college in San Fran. I've been here since Aug. 28th how ling will it take to become a CA state resident? oh and i am 18 yrs old and i was born and raised in the US.