Back-to-back bar charts like this are frequently used to compare the age distribution of a population, either of the same country but at different periods of it's history, or of two countries.
They are called population pyramids. In this case they are grouped in intervals of five years, but other intervals are possible.
Q1. What is the most obvious difference between the two pyramids?

Q2. What do you think each one will look like in 30 or 40 years’ time?