Since the mid 1980s, the median age in Italy has gone from 34 to 46 and the trend is accelerating. This is despite massive immigration. Expect this to happen everywhere in the next 40 years. India and China are already below replacement. All of LatAm, Europe, and South East Asia as well.

Unless someone thinks of a democratic, scalable solution it's going to be a lot of pain for a lot of people for a long time.