Surprisingly, after 23.5 years with this department, and 10 years prior military, I'm a little pensive about entering the retired mode. I'm certainly excited about the upcoming traveling and never having to work again but it's still a weird feeling and I'm still mentally adjusting to the idea. I find myself noting the "last times" like the last time I will have to wear a tie in uniform was yesterday. My last staff meeting will be tomorrow. 
You have my understanding with regards to how big a decision it is to retire. It is as difficult a transition as getting a divorce or so I have been told. Your coworkers will likely ask you what you plan to do. Don't feel like you need to commit to anything, just leave it open as to how you will use all that free time. You will be fine. If you get bored, you can always volunteer at whatever interests you or go back to school and only take classes for the fun of it because you aren't preparing for a career like when you were in college as a young person. If you workout, you will have so much more time to go to the gym and you can go when it isn't busy.
It took me two years and seeing a psychologist for awhile to work through my retirement fear, which is basically fear of the unknown. I've been retired for 6 years now and I can honestly say that I have no interest in returning to work. The best thing to be about retirement is that I get to do whatever I want with each day. There was some fear of not having enough money. What a joke! My retirement income exceeds what I made when working.
