Affluence...most people now have more disposable income than in years gone by.
Availabilty...food is everywhere now. During the last 50 years the growth in supermarkets and fastfood outlets has lead to this almost grazing way of eating.
I'm in my early 60s now and have always done some form of exercise. Whilst all my family/friends have health problems associated with smoking/drinking/lack of exercise I enjoy good robust health.
I take no prescription drugs or have any health issues. I do have general aches and pains that most would expect at my age but I feel that the years of exercise have helped in maintaining my fitness/balance and co-ordination and I intend to continue because I that is part of my lifestyle.
Most of my family/friends think I'm slightly loopy but they suffer ill-health and chose to follow the sedentary life that leads to poor health and dependance on drugs in later life.