The occupation structure of any place is mainly grouped into 3 parts :
Primary the producing sector
secondary the utilizing and manufacturing sector
tertiary the sector that provides services
the age composition of a country affects these sector by determining the size/number of people who can be dispensed into each.
the age composition of a country spans over four main groups
the babies way too young to be productive. kids from 0 - 14 yrs
the adolescents the future human resource and potential present resource they range between 14 - 18 yrs after which they are adults
the adults the main (legal) work force (before becoming an adult they usually start out as illegal child laborers ) these are the people between 20-60 yrs
by 60 they usually retire
the aged , they along with the babies are called dependents as they no longer work or in the babies case never worked to begin with