Is it safe to meet a young girl online?

I know the basic safety precautions but i am worried about LEGAL issues for me. How can i make sure it is not some type of sting operation? Im not entirely educated on how those work, we are just going to hang out to be friends we didnt discuss anything ual. I am worried because she is young she is 21 which is pretty close to under 18 and i heard for the dateline stings they use decoys who are actually 20. But the thing is she and her myspace say she is 21, i feel legally this should be fine especially because i am only 20 myself but is there anything that should prevent me legally? i think i am going to flake cuz im worried