If you really want an airsoft gun, just get checked out. Prove you're over 18, go through the process.
Then you really must learn about the rules/laws surrounding the ownership and use of Replica guns. Just plinking, in most places, is out of the question.
Please read some more of the FAQ? The answers are there, so are the solutions?
After age-verification, you'll also have access to the Classifieds section. Lots of stuff to buy there.