Actually you are incorrect for it is only with the passage of time that one gets passed the hormones of sex and learns what REAL LOVE is.
For some this may be 10 years, for others more, still others may not have the luxury of their entire lives together as death parts them too soon.
The analogy of "old and grey" is one that most understand to be a "very long time" which USUALLY means that as an individual or couple you've pretty much seen it all... that's all.
nothing more and nothing less.
If you marry in your 20's and are still happy in your 30's does that mean you don't know what REAL LOVE is? Not necessarily. You may know better than most, however, you are both still young enough in your lives that life might still bring you tests that what you have learned may just not be enough for you to remain together HAPPILY as a couple. Just because a marriage is intact (as in not divorced) doesn't mean that it is happy.
Do you see what I am trying to say?