Ok, I'm 18, and about to turn 19.
First off, anything less than 30 to 40k, you are not going to be able to do trading of stocks.
There are too many disadvantages.
First off, you have to have 25k to daytrade. One rule that prevented me from being a stock trader. Second off, taxes on stocks are insane. Commissions on stocks are also somewhat harsh unless you have a good broker.
Instead, a strong suggestion is to go to Futures.
With Futures, you could open an account with as little as 2k, and you can trade to your hearts content.
YM for example, each tick is worth 5 dollars.
It's good if you can trade, it'll kill you quickly if you can't manage risk or control emotions.
But unless you have 25k, you can not day-trade stocks, and I wouldn't even bother without 25k, unless you are specifically doing trades that are longer than a day each.
Just my advice, but hey, I'm only 18, so what do I know?
EDIT:
Using a Direct Access Broker is pointless, again because you don't have 25k, and therefore, can not do the required volume to keep the platform free, so it is very possible you'd be losing money.
Again, either save up so you have around 40 to 50k to trade stocks, or start out with 2k, in a futures account.
I'd recommend
www.greenstreet.com. 4.30 commissions, and hidden fees or anything.
If you are going to be daytrading, your only option is Futures, or Forex.... maybe Options, I don't know anything about those though.
So do your research, and realize, that there is a chance you will lose all of that money, so only be sure to get started if you are willing to accept the fact that you can lose all that money, and the markets can prove you are not trader material.
EDIT: If you do decide to trade stocks, you will be swing trading, and don't get a Direct Access Broker. Do not go to E-Trade, they WILL screw you over just like me and many many others.
Scottrade maybe. I have Ameritrade, but not happy with the platform. Genesis Securities is the one I have been looking at, you should call them up and see how that works, but again, they may require day-trading to avoid platform fees or whatever it is they got.
Just letting you know all of this from personal experience. I have lost money, so hopefully I can help you not lose money, but the best education you can get about trading the markets, is just going out and doing it. I was very fortunate to get a full-time mentor and he teaches me and a few others for free, and not many people will ever have that chance, so keep that in mind as well.
But here are a few questions for you, so maybe others, or myself can help you:
1. What do you want to trade? (Stocks, Futures, Forex.... anything)
2. How often are you going to trade? (Every day, all day long, part of the day, any restrictions)
3. Are you going to day-trade, and if so, you do realize that for stocks is 25k requirement?
4. What is your main goal from trading? (Looking to do this as a career, or just something as a side job or what)
5. Any previous experience in any trading market?
I think if you answer those, that others can help pinpoint what would be good for you. I again, must suggest futures, but realize that the reward is far greater than trading stocks, but the risk is also many times higher as well.
Do your research, and read about the markets.