Well first of all, one time when I was in Coffee Bean and Tea Leaf, I saw something written on a blackboard there, "It's better to do something you like, than something you're good at." That quote has stuck with me my entire life, it's really great advise. If you want to paint, then you should paint, don't let anything stop you. You should fuel your passions, embrace them, make them your own.
As for not being very good at it, well, there's several things to say about that:
• Just make sure you paint as much as you can now, get lots and lots of practice, that way when you're grown up, you'll be a great painter. Practice makes perfect.
• Make sure you take some art classes. They offer them at almost every school, plus you can take them in like, community centers, boys and girls clubs, etc...
• You're always going to think your paintings aren't as good as they real are. It's natural for humans to think the product of their own labor isn't as good as someone else's when it really is. You need to find some friends who are really really really honest, who won't tell you they like your paintings just to spare your feelings, but who will tell you if something sucks. It's very hard to find people like this unfortunately. You need to be mature about it though, if someone tells you one of your paintings sucks, don't get hurt, don't get defensive about it, just ask them what they don't like about it, learn from your mistakes, improve on it, and grow as a human being.
• Even the internet can help with this, just google "painting tips" and search youtube for "how to paint" there's great resources all over the internet with advice from the most rookie painters to even professionals.