Give Satisfaction

Reading some fics and watching some old movies, I found myself wondering: do people automatically start the tongue action on practically the first kiss? Is it inevitable? Or do people keep their mouths more or less shut for a while or maybe even for the first make-out session?

In old movies they were not allowed to french kiss, so even when there was ardent kissing mouths stayed closed. Is this at all realistic? Does it matter? Would you have a problem writing a kissing scene without tongues? I'm pondering writing one. But I've been kissing the same person for years.