Population ageing is primarily driven by enhanced longevity. Improvements in medical care, diet, and living standards allow individuals to live longer, thus increasing the proportion of elderly people. This demographic transition results in a higher average age for the populace.
While an elevated birth rate could theoretically counteract population ageing by increasing the younger demographic segment, it is not the principal contributor. Furthermore, a sedentary lifestyle affects individual well-being but does not directly alter the age distribution of a population. Lastly, migration impacts population composition, but its influence on ageing is contingent upon the ages of those migrating in and out.