I would think that you could discuss it with him - explain that you're not 100% comfy about him seeing your girly bits so he would have to stay away from the business end. I would think that if he's in his 70's he's probably not to keen on looking anyway. Guys from that era are often a bit more uptight about nudity than younger guys IYKWIM.
If you do invite him maybe you should leave yourself an escape clause - explain that until the labour you can't be sure exactly how you will feel so its possible that you will ask him to leave.