In volleyball, you can usually play for your school, but if you want to play outside of school, you may have troubles finding a league to play for. There are probably a couple leagues in Houston, but how close to the city you're in will vary. I mean if you really wanted to play, you could drive the extra distance to go there or you may have to convince your parents to take you if you can't drive.
To find volleyball leagues in Houston or any city really, just look in the newspaper, watch for flyers at school or posted around the city. Also, if you want to play indoor, Houston offers facilities at the West Houston Indoor Soccer for you to play. You can either register as a team or individual to play on a league. There leagues range from adults to the youth.
If you can't find volleyball leagues in Houston, and you don't want to try another sport or drive, you need to keep your skills up for the following school year. You could do some volleyball drills if you had the place for it and if you were a setter, you may want to try going to some volleyball setter camps on the off season. But remember, no matter what you decide, you must always improve your skills or you'll be left behind!