Start with a smaller step
You are getting some great advice. I did an extended travel through SE Asia for 7 months, and travelled with some who had been on the road for 2 years. As you haven't had any foreign travel or extended travel, you might want to plan a break-in trip. My comments:
1. Retirement itself is a major change, and you should give yourself time to adjust to your new status and finances. A year wouldn't be too long to wait before a major trip. There is no need to rush off on anything.
2. A break-in trip of 1-3 months would allow you to begin to understand yourself and how you like to travel, without having to sell the house, etc.
You don't really know the basics, and you don't yet know what your style and level of comfort (physical and financial) is. You can learn a great deal from books and travel boards, but you also learn a great deal from fellow travelers. And there is no substitute for experience. One month will just get you out of the vacation mode, and 3 months might give you an idea of what extended travel entails.
3. If you want to think about foreign travel, I'd recommend SE Asia. Can be fairly inexpensive, lots of travel infrastructure for English speakers, lots of other travlers to get advice from, great food, great culture and history. Lots of natural beauty.
4. There is nothing wrong with starting with a group trip, to see some sights, then taking off on your own, when you have an idea of the area. As others have said, loneliness can be more grating than physical deprivation. You can also plan a couple of group trips, and do independent travel between them.
5. I's recommend you start reading the Lonely Planet guides, and start looking at the Thorn Tree posting boards on Lonely Planet. There is a long-haul board, but there is also and older travelers board. There was a poster on older travelers, Packerjohn, who had very interesting commentaries. Even he got tired of the road and is back, in Canada, I think.
6. There is no one way to do this. Finding those places that you dreamed of as a kid is one way to make a list of places to go.
7. Make sure you plan for problems. That includes medical evacuation insurance, medical insurance, proper vaccinations and indicated medications, care of your properties and investments while you are away. Making sure you start in good health is also paramount.