I'd recommend that they not be afraid to tell the FAs that it's their very first time flying. It's relatively rare for people in their 60s to have never flown, and I'm betting at least one FA will be intrigued and help them through all the little questions on board. They might even do a PDB.
If an Airbus, you can tell them that the plane may shake a bit on takeoff, but that's normal just before the landing gear comes up. (On a Boeing, this isn't an issue, but I have had seatmates raise their eyebrows over the shaking that can occur on Airbii.)