Here is some advice from someone your ages.
Im 18 and ive been chasing storms for 3 years now. I am now an intern for the amarillo national weather service and im going to Texas A&M for meteorology this year. The best advice I can give you is be smart about everything you do. Don't be one of those "chasers" who I hear about being killed because they had no idea what they were doing. Research research research, know what you are doing. Ask other chasers for advice, talk to the forecasters at your local weather service, and most importantly never chase alone.
Become a ham radio operator. Get your tech license and learn how people in your area chase using ham radio. My advice is never never never never never chase without first having your ham license. You will be going into areas that may not have cell service due to damage. If you are in a life threatening situation and you need help, ham radio never fails.
You need money, and lots and lots of money to chase. My advice, see if you can get someone to pay you to chase. This includes TV stations and company's wanting stock footage. You will need to be 18 before you can be payed to chase however. This year since I am 18, KVII in Amarillo is paying me to chase for them and we will also be selling footage. You must find a way to make money chasing, or you wont be able to do it very long.
Don't make storm chasing something you want to do the rest of your life, go to school for meteorology or atmospherics sciences, that way you can get payed doing academic research, which is basically storm chasing.
As I said, chasing is extremely expensive. Here is a list of equipment:
Gas: $500-1000 per year
Car Insurance: $100 per month
Windsheild replacements (for those times you miscalculate)~$500
Radar/Allison House Data-I recommend Gibson Ridge level 2 and 3. We use both at the weather service~$500+$10 monthly
Training!!! GO TO SKYWARN TRANING ITS FREE
As you can see this hobby, which is what it is until you are doing it for money, is extremely expensive.
When you are chasing, its important to clearly mark your chase vehicle. Just because you are "chasing" doesn't mean a cop wont pull you over for speeding. However if you clearly mark your car, have caution lights, cops will leave you be provided you know what you are doing and are not being reckless while speeding. Cops are your best friend when chasing, they will pull up to you and advise you of what they know. Don't anger them.
Know what you are doing, be safe, don't be an idiot. If I see you on the chase and you are being dangerous, I will personally pull you over. I have done it before, and they were teenagers. You can and will receive a citation if a police officer is near by. You are endangering the lives of everyone around you.
This is a wonderful but dangerous hobby. Have fun and be safe on the road.