Don't listen to these guys. Yeah, you can't technically day trade on Robinhood, but you can still make short term trades.
The best advice I can give is make sure to place limit orders when trading lower volume stocks. If you place market orders on low volume stocks you could get a really bad price. Try to stick to more stable stocks. Yeah, you can make quick money on risky, small stocks..but you're more likely to make money (and have fun) short term trading more solid stocks.
As for platform, use Robinhood for sure. You can't pattern day trade until you have $25k, but you shouldn't be doing that until you get more experience anyway. Just get your feet in the water and test it out.
If you're also looking to start a retirement account just set up a Roth IRA on another site and put some money into low fee total market ETFs or something similar. Hmu if you have any questions about that also, very very good to start young. Have fun!
While you're at it, use my referral for Robinhood when you sign up and we'll both get a free stock:
http://share.robinhood.com/johnh595