Casual Sex?

I had a conversation with some friends the other day about casual sex. They both had very different opinions on the subject... I don't really have much of an opinion at all. Is it okay to have it, or is it wrong? How old should you be in order to have casual sex? All of these questions just confuse me. Does it make you a whore to have casual sex when you're under 25? Does it make you a whore to have it at any age? Don't get me wrong, it's not for me. I pride myself  because of my morals, but those are MY morals. I don't really have a problem with what anyone else thinks. I just wonder, if you are having sex with someone over and over again and it is only casual... don't you think that it might end up not being so casual? Someone could very possibly get hurt, even if you both go in agreeing it IS just sex, or what if it's someone no one would approve of, what if you or your casual sex partner get pregnant? All of these questions honestly scare me out of having sex in general. I just want to know what other people think.