Far more than AI what would be needed is a robotics revolution. AIs may make decent “fake” brains, and especially task-specific “fake” brains. And right here in the now or immediate future.
But a shrinking human populace (and especially an aging shrinking populace, as you pointed out) will need “fake” arms & legs to perform the labor the AIs may decide needs doing.
Right now humanoid robots are far heavier and more power-hungry than humans. Certainly there are many activities (e.g. in factories) where humanoid form might be handy as an interim step to replace the human workers without retooling the assembly line. But a more holist approach would then retool the factory to where humanoid form is an obstacle, not a benefit.
But there are many activities where roughly human form and roughly human mobility will be near prerequisites to the work. And that’s a tall order mechanically, even if we could endow the machine with a near-human-equivalent silicon brain.