Retirement is just around the corner. Any fitness tips for the aging military athlete?

Become an MMA fighter.

Leave your Rank in the safe with your DD214. No one cares if you're an EX SMaj, Maj, or whatever. Retired Generals are a different story.
Expect to start at the lowest rung on the ladder. Some places will use your Military Experience and start you higher up the ladder, but don't count on it,
Advancement is what you know and what you do, Not who you know.
Starting pay and your retirement pay should exceed your active duty pay.
Don't tell your supervisor, We did it this way...... He/She could care less.
Keep fit, keep up with the exercises, etc., your not a young chicken anymore, your pushing the "old goat" category.
Depending on your new job, don't go "native" or hippy, unless everyone in your work area does it. Remember, it an 8:00AM to 5:00PM job (or 8 hrs with a lunch break and some regular breaks during the day). Getting in early and staying late will get other workers pissed off at you unless you are offered overtime (interesting concept the Military never heard of).
No such thing as :"sick call." If you are sick call in and go to the Dr.
If you are around a Military Base, you can use those facilities and not Salute that Newly Minted 2LT or an overbearing Colonel.
ENJOY YOURSELF. Remember, telling your supervisor to "suck off" will only get your fired, (unless you belong to a Union) not jailed, unless you punch him/she out. (Not advised, no JAG for a free Lawyer).

GOOD LUCK. (this was fun)

Stay active.

COL Lee Flemming I can't give you the tips that 1LT Sandy Annala Gave you below that is for sure - awesome information. I can tell you that since I've retired I've gotten a full physical by the VA each every year (4 years now) and I walk about 3 miles every morning in between posts, responses, votes up, new connections, endorsements, and admin duties on RP. It has kept my weight in check and my blood pressure good and I still look damn good for a 59 year old! No vanity intended Lee! Good luck on your upcoming retirement!

But not the end of the road, unless you decide to sit and vegetate. I retired with social security benefits in 2015 took some time off for about 8 months having fun. I now have started a new venture as an Uber driver and have never had so much fun sitting on my ass making money, but more importantly meeting interesting people from all walks of life and hearing their stories. Maintain your good health and enjoy life to it's fullest, travel some do the honey do list and go on from there.

When I first retired we took 3 months and went to Europe, backpacked and toured 5 countries. Needless to stay my wife and I had no trouble staying in shape WALKING and traveling everywhere. Then we returned to the States. Hopped into the RV and traveled for 2 years. Sittin on your butt and traveling by driving, Walking occasionally and touring a bit while walking dogs, is not the same as backpacking through Europe. Weight gain creeped up. Beware of unintentional loss of activity while still having a blast touring and enjoying your retirement life. Plan and keep a exercise regimen, it does not have to be the same as your active duty life, but has to be something. When on Active Duty I got up EVERY day and ran at least a few miles. Now as my knees no longer work that well at 70, I walk a mile or so twice a day and swim 3 to 5 times a week. As life progresses, change your routine. BUT do something.

COL Lee Flemming Maintain your medical records and medications for disclosure to new doctors. My Apple phone's HEALTH app has a great deal of my medical info. I continue to hope the paramedics; if I punch 911, are familiar with them not needing a password to access the app!

Take a well deserved break for just a few weeks!

Keep your mind active, your smile wide and your heart warm!

Best Wishes for a healthy happy and enjoyable retirement! Thank you and your family for serving and all the sacrifices.

Flexibility is the fountain of youth :)