If intimacy and passion is needed to keep a relationship, what happens if they both get old?

I've heard someone saying that as long as there is intimacy and passion, the relationship remains alive.

But after many years later, both are going to age. What about couples ages 60+ years old. They already lost their youth and obviously both have wrinkles by then. Is just intimacy and passion all that's needed to sustain a long-term relationship or marriage? Doesn't the infatuation stage fades at some point? Are you really going to live your life forever base on intimacy and passion?

If intimacy and passion is needed to keep a relationship, what happens if they both get old?
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