Reply to New dj with questions

I am new to the dj scene. I always loved djing and decided to make a serious effort into learning the art. I find myself running into a problem. How do I go about getting a good collection of music? I'm in my 30's so there is a lot of old school stuff hip-hop and house i would love to have also stuff I won't remember until I hear it. Any sites that is recommended or should I look to buy a HD from a dj selling their music?