Meenamehta, I am younger than you, mid-60s, and also walk regularly. I also live in a hilly suburb, but due to altitude issues I found all of the mountain areas in Switzerland very tough. I am very pleased we didn't have to do added hills to and from the hotel, although other posters are right that it is only a gentle slope. There are so many gentle slopes though!
We only did the hike from Murren to Gimmelwald. We also did the one from Mannlichen to Kleine Scheidegg, plus one at Schynigge Platte which I found really tough.
There was limited food at Pension Gimmelwald, from memory there was a toastie that looked really good and a couple of other snack style things. We just had drinks.
We didn't do the Berg cliff walk as the website stated that it was closed. As our gondola sailed past it on the way down, we saw that it was actually open, but by then we had plans for Murren and Gimmelwald, so it was too late. I don't feel we missed too much as we did the one at First and I am sure they would be reasonably similar. There simply is not time to do everything.
As for our drinks at Piz Gloria, that was all a bit of an accidental muckup. We somehow entered the restaurant at a back entrance, there were no queues and we had no reservation. There were lots of empty tables as it was just after 11, so a bit late for breakfast and too early for lunch. Some tables had a Reservation sign so we ignored them, obviously, and sat at a completely empty table right by the window.
Shortly after the waitress came around and we ordered two glass of Bollinger. Of course the restaurant is constantly revolving, and we got to see virtually all of the better views before we moved to an area with a massive queue of people. A man came over and asked how we had got our seats and who seated us, so we told him. At that point he said we'd come in the wrong entrance and would need to join the very long queue, also that no window tables were available without a reservation. Oops.
Luckily for us, right at that moment the drinks arrived. Once he saw we had ordered, and paid for, Bollinger, he completely changed his tune. He said if we moved to the other end of the table we could stay and have our drinks.
I do feel if we hadn't ordered, or had just had water or a coke, he would have made us move. Hardly fair, but that's life I suppose. It was a genuine mistake on our part. We finished our drinks and left, which was what we had planned anyway, and luckily we had seen the views by then any.
So long story short, if you want to go you should book, but I don't think you can just book for a drink.