To the OP - is there something else you would like to do? Do you have any entrepreneurial desires? I'm just over halfway to a military retirement but this is a second career. I fully intend to start a third phase for about a decade after the military before fully retiring in my mid 60's. I do enjoy what I do but I'm tired of moving. I enjoy traveling and we intend to spend 3-6 months on the road in the RV one day but relocating the entire household every 2-3 years has gotten old.
My youngest will finish college the year I am retirement eligible from the military so I'm looking forward to finding that oil well in my backyard. :)
I'm in the camp of getting bored if I don't have a solid plan. Last week on leave at home for Thanksgiving about drove me crazy because I didn't have projects. I know that I either need to retire in the country with land and a big workshop or a city big enough to have regular events. I expect the projects will occupy me better. My dream is buying a homestead that I keep for the rest of my life and traveling during the poor weather months at home which would be two blocks per year.
I also intend to write articles for journals which I can do from anywhere that I have online access to research and maybe historical fiction that no one will read but I'll have fun writing. Photography will be a regular hobby, hence my moniker, but I know that I would be bored doing it every day. You have to think through all the variables.
Last bit is preparing financially, which as others have stated it helps to start early. I've always saved aggressively assuming that I won't be able to complete 20 years to get a pension or the govt will decrease the pension. If I get it, I'll be set for substantial travel. If not, I'll still be OK.