With the rest of the developed world (outside of the US and a few others) moving into aging demographics more-or-less all at once, export-driven economies are going to be hard-pressed as global consumption decreases in the developed world. They also won't have time to experiment.
Now sure, theoretically governments could learn from Japan's successes and failures and, being forward looking, could initiate policy 5-10 years in advance to offset the worst of the impacts and... sorry I just laughed into my keyboard. It's going to be a show, people will wake up one morning, stuff will be expensive and broken, no one in power will understand why, problems will be denied for months until things break beyond the point of no return, and the solutions will be rushed, poorly directed and half-assed. See Germany's current energy woes.
Germany, South Korea, and others are going to hit the same problem in a much more hostile global economic environment, as most of the wealthy global consumers are going to simply disappear. At present they're woefully unprepared to deal with any of it.
That's not what the propagandists claimed though.
> That gave it advantages and opportunities that won't exist for many countries once the developed world at large ages into mass retirement
What unique advantages and opportunities that won't exist for others? This sounds familiar.