וַתִּצְחַ֥ק שָׂרָ֖ה בְּקִרְבָּ֣הּ לֵאמֹ֑ר אַחֲרֵ֤י בְלֹתִי֙ הָֽיְתָה־לִּ֣י עֶדְנָ֔ה וַֽאדֹנִ֖י זָקֵֽן׃
And Sarah laughed within herself, saying: ‘After I am waxed old shall I have pleasure, my lord being old also?’
Read kabbalistic (mystical) interpretation of Genesis 18:12: and classical mystical sources.