Regarding age, you'll be fine. Windstar attracts a slightly different demographic set than other cruise lines. Recall that these ships have no elevators nor any type of handicap facilities, so, by definition the passengers are relatively fit and agile bunch, nevermind the age. Also recall that the ship is very informal with no dress-up nights, which also attracts a fun, casual and active crowd. Sure, you'll be among the youngest, but if you don't mind being kidded about it, you'll get along fine.
We did Windstar in the Carribean this spring, before it relocated to the Med. Fantastic Captain and crew. We enjoyed hanging out in the lounge after 7 pm when the most of the passengers took off for dinner. There we could hang out with the Captain and some of his officers for a beer and a chat, hearing all kinds of great stories and cruise jokes.
Great ship for a honeymoon - very romantic!
We have done the Rome - Nice itenerary on the former Rennaissance line and loved it. You will really appreciate being on a small ship when visiting the smaller ports along the French and Italian Riviera.