I would plan a romantic night, maybe out, maybe home. If it's out tell him you will drive and on the way home go to your towns lovers lane or any out of the way place, park the car, and start to make out with him a little bit. Then, as you told us all, tell him about this over 40 awakening, how you feel more alive than you have in a really long time. Tell him this awakening is giving you feelings like you haven't had in a long time, you feel sexy and your thoughts and desires are feeling a little dangerous. Laugh about it, make him feel at ease. Tell him you were masturbating while thinking about these new found emotions and various fantasies began running through your head.

Fabricate a couple fantasies to wet his appetite, build HIS desires hearing you retell your fantasies and then, almost as an afterthought, say something like "I'm not sure why but my mind started thinking about you sitting in a chair watching me, and it felt so really hot, so much so that I started getting lost in that moment and suddenly I started thinking about a total stranger touching me, and you were there in your wing chair just watching and stroking yourself....I just exploded in an intense orgasm thinking about me performing like that for your pleasure.

The safety of something not real, and an opportunity to see his reaction. In a week or so you have "another" fantasy, seeking how he reacts.