I think its fine to have sex before marriage. It seems to be a common part of society today. Sex before age of consent happens, theres not really anyway of preventing it.
It's all down to personal choice though. If someone wants to save themselves for after they are wed then thats fine. If not, thats fine too.
The most important thing is that people who partake in casual sex use protection, contraception and have regular health check ups.
~ The journey of a thousand miles begins with a single step ~
* Nothing in the world has ever been accomplished without passion *