Here is my prescription for maintaining vigor in old age: Start by acknowledging this is you at this age right here, right now.
1) Maintain mental alertness and function: read history or whatever you like, learn a language (to speak a language you will need a partner in the work), learn a new skill such as electronics, RaspberryPi computing (use You Tube), astronomy, quilting, et.al.
2) Maintain physical strength, in fact, optimize it: e.g.,walking, lifting (light) weights. I enjoy Planet Fitness and fortunately is is only about 1.25 miles from home. Use exercise to lose weight if needed and this will make you feel better too. We do a non rigid paleo diet and I think I feel better and don’t so easily put on weight on this diet.
3) Develop flexibility: Inflexibility is one of the most often heard complaints about old age. You can fix that with Hatha Yoga. I recommend AM yoga on DVD (do it anytime) by Rodney Yee or find a course at your local hospital or YMCA, etc.
4) Maintain social interaction: being married (happily) is good for your health, but expand into other areas. Where? Start with what is of interest to you and find a club. If nothing is of interest then join a volunteer or service organization and help others (or, do this anyway as it is an excellent way to improve mood and sense of belonging).
5) Review your medications with your doctor: some you may no longer need; some may have adverse side effects that could be moderated or removed by a change of therapy.
THE MOST IMPORTANT PART IS TO GET INTO ACTION