In many situations, you may need to put the count or cases together with the percentages into one cell in Excel.
=B2&" ("&TEXT(C2,"0%")&")"
Where B2 is the count of the people in each age group, and C2 is the percentage of the total for each age group.
TEXT(C2,"0%") is to keep the percentage in the percentage format.
To separate the number and percentage, please refer to how to separate number and percentage from one cell.