Question
My mother is 80 years old and in very good health. My siblings and I do not agree on her lifestyle choices, particularly related to eating. I am of the opinion that at that age she should do whatever she wants. The time for watching your diet is over and she should live it up. My siblings think that I am nuts and that healthy eating is a lifetime sentence.
        I am more of a live and let live kind of guy, where my siblings are a bit fanatical about diet and exercise. I suppose all that matters is what mom thinks and wants to do, but this subject just keeps coming up. Frankly, I am a bit tired of the discussions.  

We have all agreed to let you be the deciding voice on this subject of diet and exercise. I am hoping that will put this discussion to rest once and for all.

Answer
Okay then, you and your siblings are in quite the debate over the lifestyle of an 80-year-old and I am going to be decision maker.  
        My first thought is that an 80-year-old whose cognitive abilities are intact is likely going to make their own decisions about what they eat and how much they exercise. While the children may have many varying opinions about what their parent should do, it is really up to her to decide. The interesting thing is that as we mature and our parents age we tend to feel that we can advise them on a variety of topics. I am not sure that they always appreciate our ideas though and may feel that they have accumulated 80 years of knowledge and you do not know more about anything.  
I am certain that your mother has firmly established patterns for movement, eating, sleeping, and so on. While it is possible to reformulate your lifestyle in your 80’s, most people will not.   

To help resolve your debate I have listed my thoughts below:
• Everyone should engage in regular movement within your ability.  Walking, swimming, yoga, weightlifting (mild), stretching, core exercise, and many others.  Pick a varied field of activities or exercise regimes that keep the body moving and strengthening focusing on the entire body not just one part.  Do 30 minutes of something every day.

• Diet is simple.  Everyone should eat low fat, unprocessed, whole, high fiber foods as the basis of their diet regardless of age.  Desserts, prepared, and packaged foods should be kept to a minimum.

• Weight should be within the Body Mass Index for your height.

• Get a good night’s sleep of seven to nine hours.

• Engage in meaningful work.

• Socialize with family and friends.

• Get a checkup once a year.

I do not believe that the formula is complex and that most of us do not already know how to live a healthy life. There are many temptations in our society that can take us off track, and occasional variation is just fine.  For a long healthy life on average, I would follow the recommendations above.