Answer:
heterogeneity
Explanation:
A population can be similar in traits or it can be different in nature. The populaiton which is diverse in traits is called a heterogenous population while a population which is similar in traits nature is called a homogenous population.
The traits can be the language they speak, the skin tone of the people, the religion they follow etc.
Here, the statement describes how aging is different for different people in the same population hence this refers to the concept of heterogeneity.