I'm an atheist, more specifically both a secular humanist and a naturalist. I've never seen any reason to believe in religion, not even when I was young. Heh, I remember when I was in Primary School making up gods similar to the Invisible Pink Unicorn and Flying Spaghetti Monster to troll gullible people. To be more specific as to why I'm not religious, for me it's more a case of 'why should I be religious?' than it is 'why shouldn't I be religious?' as no arguments for religion have ever made sense to me, most that I've heard are based on complete myth, 'because I said so,' emotions like fear and similar things. If there was genuine proof of a religion being correct, I would join a religion. Old books with content that cannot be proved in a real scenario, unlike say, a biology or chemistry textbook, is not genuine proof. If you read about a chemical reaction you can probably replicate it. If you read about evolution you'll find that there are modern examples of it, although unfortunately I can't find any at the moment. I do believe there was one involving worms or something like that, they evolved to live in an area of contaminated land that was hazardous to worms of the same type that hadn't been born in that area. I can't remember exactly what it was, but that's the gist of it.
Edit: That's the philosophical methodological naturalism, not the nature worshipping naturalism.
Edit: That's the philosophical methodological naturalism, not the nature worshipping naturalism.