My first aparment. W/ my sister.?

I'm not old enough to move out or even get a job yet but when I do I'm going to save up for an aparment. My sister is three years younger than me and she wants to move in w/ me. I told her that that was fine but she had to hold up her end of the deal buy helping to buy half of everything. I also agreed to wait for her to turn 18 so I won't be moving out until I'm 21. My question is about how much on average would we need to save up to be able to get an aparment that is about $800-$900 monthly. And also about colleges. I want to be a zoo keeper and she wants to work in the aquarium, but we were wondering if it would be better to go to college or to take online cles. And also if going to cles are better are there any that offer zoology and marine biology at the same school?