On one hand, perhaps they have grown tired of making idle chitchat over their decades together. Maybe it has all been said and done, and they don't feel the need to eradicate any silence between them. Think of how this paradigm develops throughout a relationship; going from constant nervous chatter on a first date, to a comfortable back and forth where you can finish each others sentences before eventually turning into an elaborate system of clicks, pops, grunts and pointing.
On the other hand, maybe it is possible that this old couple has been together for so long, and are so completely intertwined that they have developed a kind of old couple telepathy. At one point during the meal, the old man was looking at a young mother getting her baby ready to leave the restaurant, and he smiled. Upon seeing his smile, the old lady turned in her seat to see what he was looking at, and she too smiled. She turned to face him and as their eyes met they nodded at one another. In that moment they could have been saying any number of things to one another:
"Remember when the kids were young sweetheart?"
"Oh to have the energy necessary to take care of a little one again."
"I can't wait till the grandkids come over this weekend"
"God damn that MILF is hot! And thanks to the little blue pill, now I can take you home and screw you till one of us breaks a hip while I think about how cute her ass looks in those jeans."
You know, something like that. All joking aside, I can see how this geezer telepathy can develop over time. I've been with Inky for 12 years and we already have a bit of it going for us. God knows we both end up saying the same thing at the same time offen enough that it borders on the creepy. I have to think that in time I will be able to just look at her and she will know what I'm saying, and vice versa. I just hope that I find a way to avoid the billowing gray nose and ear hair that seems to come with that power.