I agree realist, but look at your parents and grand parents lifestyle. What jobs did they do, did they have to do a lot of manual labour and physical jobs. Did they have to walk to do things and to get places.
My own father who is approaching 80, never did any structured exersising or dieting in his life, but was always extremely fit and very strong. In fact, his dinner plate was always stacked to the edges with huge amounts of food, which he never left any of. All this was simply because he worked on building sites all his working life. My mother, was always fit, because there waas only ever 1 car (and my dad used that to get to work all over the country), so she had to walk to the shops, and walk us to school, or even walk half a mile to the bus stop. This kept her fit.
Todays lifestyle is the problem why people need to keep fit as a leisure activity. Computerised robots doing repetitive manula labour, everyone having a car at their beck and call.
If you go back further with your relatives, you will probabbly find more and more of them were quite a lot fitter than you and me.