This table gives an overview of the age structure in the Brussels Capital Region and its 19 municipalities (by gender).
It breaks the population down in age brackets of 5 years. It also shows the evolution of the amount of people in the age categories 0-17, 18-64, 65+ and includes the average age.

It also contains data on population growth by age divided into 3 groups from 2000-2020 (on 1st of January).

A file on methodology is availably through the same URL source.

Both files are also available in French.