"Let me not to the marriage of true minds/ admit impediments"
The phrase "true minds" suggests an elevated rather than physical love. With a love of this kind, no obstacles should interfere. A marriage of true minds should withstand any storm, including the ravages of time. This type of love is unchanging, an "ever fixed mark". Unlike other loves that could be tossed about by tempests and destroyed, this love is solid, like the star that guides the lost at sea (every wandering bark). Because it is not a lust or a body driven love, the usual mortal complaints don't apply. Time may ravage the body, affecting such external qualities like the rosiness of lips and cheeks, but a marriage between true minds--that is true, exalted love--will continue despite the ravages of time. And this is what it means to love.