Such an example like your granddad-in-law I have also from my grandmas village where we had a neighbor that lived up to 90 years old and worked his entire life in agriculture. From the end of May when the temperatures were starting to rise until September you would only saw him in the evening wearing a cotton shirt. Otherwise he would be on the fields wearing no shirt and working from sunrise to sunset. I never ate with him, but I am sure he only ate healthy food in that time as all the villagers used to. No chemicals, no coffee, no RedBulls. It was physical effort, zero stress involved and natural food that helped him live nine decades. Nowadays there's a lot of obesity, diabetes and many other diseases that eat us alive and the only ones guilty for that are ourselves. I am amazed by myself how many health conditions I have faced in three decades. Don't even imaging living 90 year, but as long as I can I will manage my health and discovered that very often the best treatments and health maintenance ways are too accessible, easy to have and cheap to even notice them. Take the example of water. Only drinking an enough amount of water in the morning and it's like you don't need coffee. I never had a sedentary work place, like in an office, but when I'm at my laptop at home for hours I feel its side effects.