This does seem to encapsulate some of the issues that have arisen regarding directives to refrain from extramarital sex. Basically, nobody would have conceived of 30-year-old single people or 40-year-old divorced people who had been married 20 years already. I don't think God was trying to create 40-year-old virgins. So how should sexual purity be maintained when marriage may well be when one is 30, or 40, or 50? Or what about when you've been married before (or frankly, not married before) and already had sexual relations?
Also, it's not like there's a switch that just flips. First sex was bad (because it was extramarital) but then it's good (because it's marital). How is that reconciled?
While refraining from sex is going to be the best idea, can we also discuss it in the light of current western culture being a whole lot different from the culture of 2000 years ago?