Older people are most likely to develop serious illness because with time they became physically weak. The immunity reduces with time & with age the chances of comorbidities such as Hyper Tension, Blood Sugar, Reduced Calcium level or any other typical pathological deficits, can lead to serious illness. So its always better to take regular check up's as they are more likely to get seriously ill.

I hope this answer gives you some insight. Wish you a great eve!