It is very easy to adopt a sport as your exercise, even if it is your only form of high intensity exercise, especially if it is a sport you love. Even if someone does not love their chosen sport initially, with time and practice, many people grow to love and appreciate it, so it is very easy to maintain it as your form of physical exercise, even into old age.
People who play sports tend to stay fit and healthier as they age. Finding a sport early on in life, like your 20s and 30s and then sticking to it throughout your life is the key to remaining active in your old age. People who play sports tend to be healthier as compared to those who do other forms of exercises as playing sports require a specific diet, coordination, and muscle groups. Since transition from middle age to old age is a process of slowing down and dependency, playing sports can lead to fitter, healthier, and relatively independent living as you get older.
Other types of lower scale physical activity like housework, gardening, or do it yourself activities, do not stand the test of time and their benefits fade with age and time. So, sports and exercise in middle age, instead of walking and doing low intensity domestic labor in old age is more beneficial to health and fitness in old age. If playing sports has become a habit, then it is obviously difficult to break that habit and people tend to stick to it even in old age as much as their health allows them to. Even late comers are allowed to reap the benefits. Even those who take up a sport in late middle age are more healthy and fit as compared to others as sport allows them to develop the skills, planning, and coordination for a long lasting healthy life.