There are so many variables at play when it comes to just how fit and healthy one might be at age 78, (or whether one is still alive at 78) it's not even funny.
In descending order of importance to your longevity;
A: Genetics
Your family history, and how long your ancestors tended to live, and what shape they were in when they were at a give age.
B: Life-long lifestyle
How fit and active you have remained, consistently, throughout your life time?
C: Geography
Where do you reside, and what are the disease risk factors for where you have made your home?
D: Live-long substance choices
Have you avoided abusing narcotics, prescription drugs, tobacco, and excessive amounts of alcohol?
E: Life-long diet choices
Have you eaten a reasonably-healthy diet, and avoided excesses (in any given direction) of sodium, fat, and preservatives?
and lastly,
F: Recent, late-in-life fad diet and fitness choices
Being a recent convert to (pick one) veganism, vegetarianism, low-carbism, low sodium diets, Atkins, Mediterranean, Paleo, Fit-Bit, P90x, Bowflex, and Cross-Fit......
Unlikely to turn the tide of genetics, lifelong fitness norms, and lifelong diet choices.
Thanks for your time and attention.
I have to go grill a steak now.
A ribeye, medium rare.
With a nice glass of Australian Shiraz.
:lol: