What you describe is a bar chart with Country as Dimension and median Age as measure. You can create this easily in Qlik Sense: Just drag a bar chart into the sheet.
A histogram is different - it is special type of bar chart: A histogram always takes one field only as parameter - the dimension is the field grouped, like Class(Age,10) and the measure is the frequency of the field, i.e. Count(Age). A histogram will show how the field values are distributed.