Richard Dawkins and Christopher Hitchens really are great thinkers on the subject to look at.
Um, in terms of agnosticism and atheism, I really think of atheism as a lack of belief due to a lack of evidence. That is, I am an atheist and not an agnostic because I believe that there is [a] no evidence whatsoever for any of the concepts of God that I have encountered and a wealth of evidence to suggest that the religious account (man in his own image, no evolution, etc) is wrong and that a natural birth of the universe is more likely.
So really, I don't know. I think it's really a hair-splitting thing, in regards to labeling yourself. "I'm agnostic about God in the same way I'm agnostic about fairies", as Dawkins says.
I don't know that fairies don't exist but there's no good reason to do so. In that sense, atheism and agnosticism overlap hugely.
It's really muddy. xD
And yeah I'm 16; 17 soonish. Why do you ask?