Ive done 3 on my own and will do another next winter.

It all started many years ago when i had to do some business trips to various european destinations. After the first trip, where i was met, chauffered and wined and dined, increasingly i had to fend for myself. I realised how much i was enjoying the travel challenge. At this point i had never holidayed alone, but having separated from my partner, i did a 5 day solo trip to Boston in the U.S to see how i would find it. Well i loved it, you get to do exactly what you want without worrying what others may think.
As has been pointed out already, eating is the only problem.
I never stay too long in one destination, i'd rather leave thinking i'd like to go back, than start getting bored in one place.
I also try to go to places with plenty of activity, cities such as Tokyo will keep you entertained for weeks.
Choosing the right flights with the right timings and better aircraft types will also enhance the experience.
Having not done a trip this winter as the money needed to be spent on house improvements and a new car, i'm just itching to get away alone again.

Same age as you, and I used to do a lot of flying, but now I am planning to start doing RTWs solo later in the year, with two a year - one OW and the other * Alliance. I am looking forward to it enormously, and I would much prefer to travel by myself. Fortunately I have an understanding wife.

If you do the twice-annual circuit consistently, I think you'll discover two things: first, there will be countries, cities, airlines, and hotels that you'll want to include again on subsequent trips...a kind of homecoming in various seaports: nice to be greeted by name, and taken in again. Second -- and this may be partly getting older, and/or partly a function of having done the circuit so often: you'll find the discomfort that some people feel at dining alone disappears, and you'll be comfortable going anywhere you want, and doing exactly what you want. Seniority has it's credibility, and it makes travel much easier -- plus, you'll always know what you're doing, with no rookie mistakes.

How many countries have you been to?

Just 58, so far.