I have the same fantasy/desire, to get pregnant by someone other than my husband.  Getting close to being too old for us to enjoy raising another though.  Hubby is a bit older than I am too.  I had hoped it would happen with my Boss/Lover of 11 years, but he is even older than my husband and we ended our relationship during the pandemic (he got REALLY crazy about conspiracy theories).  Now that I am without a relationship outsode my marriage, all my old fantasies of a pregnancy that is OBVIOUSLY not my husband have come roaring back.  Meeting people is even more complex now, we no longer work in the offices post-pandemic and that is how most of my affairs started, with co-workers.
J (the wife)