Can I have sex without marriage?

Of course you can. If you're religious however you then may want to consider your actions because sex before marrige is not usually accepted.

Some religions tell you it's not ok to have sex before marraige, yet their representatives have done far worse to young children.
If you aren't religious I suggest you get out there and bang all women of legal age with their consent, with a condom of course.:)

Yes, of course you can, but think about whether or not it's right for YOU so you can decide whether or not you SHOULD. "Can you" and "should you" are two different questions, and you're the only one who can really answer that. Be sure you're safe, respectful, considerate, and look before you leap. And don't do anything you don't want to have to confess to your future wife one day.

Hell Yea !

This is based on your idea, feelings, and subjective thinking.