Answer:
A cross-sectional study
Step-by-step explanation:
The best fit would be cross-sectional study, for one because it is observational, meaning there is no manipulation of variables like you would find in an experiment. Secondly, it is comparing populations within different groups, in this case age groups. Although, this can also be done through a longitudinal study, but as the name suggests, it is longitudinal so it is done over longer periods of time.