A Med cruise is a wonderful way to introduce Europe to your fiancé. I went to Europe on a 3 week land tour for my first honeymoon when I was 24 in 1974. Ironically, we befriended and hung out with older couples as we found them to be more interested in the cultures and tours as opposed to getting drunk every night. I would suggest Iconic Western Mediterranean as it covers a lot of ground in a week. We liked all of the included tours, and recommend Herculaneum which is optional but not expensive. We also added (and enjoyed very much) the Ultimate Tuscany post cruise extension where we ate and hung out primarily with a young couple that didn’t seem to mind being with folks their parent’s age.