The animation here irritates me. If you change the date by five years the graph points should scroll vertically (and adjust horizontally as necessary), otherwise it just makes it harder to see how the pyramid changes over time.
Unfortunately, the way I animate this graph is very basic and I did not take time to make it perfect (the data crunching, SEO optimization and UI fine tunings already took way more time than I wanted to put in this). This is just a hobby project for me.