[ozim]

I think you read graph wrong.

If you are let’s say born in 1990 there were x people born this year.

Before 1990 there were boomers whose numbers each a year was higher so more people born like in 1954 for example 1.2x.

Nowadays less people are born like in 2015 that is 0.8x.

That is why there is still more older people even if they die, there is much less new people born than born in the past.