Answer:
Cohort
Step-by-step explanation:
A cohort is a group of statistical subjects that share a common characteristic. This common characteristic is most of the time a specific period of time, for this reason, cohorts are very useful when statistical studies that take into account different periods of time.
In this case, the cohorts are defined by their age, even if the categories are quite broad: adolescents, young adults, middle-aged adults (those in their 30s and 50s), and the elderly (those over 70). These groups are all examples of statistical cohorts.