Thanks everyone. I'd love to go back and do some proper trekking in the mountains but I would have to be careful about the altitude.
Just as I was setting off back down the mountain I passed a woman nearing the top. She had a stout wooden staff in her hand...and told me she was 74. She looked better than I had at the same stage the previous day. My only defence is that she was Tibetan and to Tibetans 10,000 feet is just a little mound.