Mmm.
The topic of retirees entering the workforce was already mentioned, and that's going to be a clusterfuck and a half. Social Security simply isn't designed to sustain that many dependents for another sixty years, so Social Security would have to be scrapped and replaced with a new system. This might be the ideal time to completely revamp social security and turn it into a sustainable system for the modern life expectancy, but I've seen how people in the trades get in their sixties. They get cranky, fed up with this shit, and they start counting down the hours to their 62nd birthday. Maybe their 65th if they have titanic willpower or need the extra benefits.
I don't know if you could convince these people to work another forty five years, let alone the fifty or fifty five that would be necessary to make Social Security sustainable.
What would take SocSec's replacement would likely be a government incentive program to save money and invest. The old "Totally not a Ponzi scheme, bro!" system simply wouldn't work without constant, steady stream of old people leaving the market and young people joining.
As for newly-young people joining the labor force, that would get fucky real quick. The young don't have the skills to compete with the also-young with a lifetime of experience, and increased consumption isn't a magical bandaid. We only need so many commercial pilots, so anybody looking to enter that field is screwed for the next thirty years. And what about farmers? You have grandparents owning the farm, the middle generation operating the farm, and the children working on the farm as they learn enough to take over when it is their time.
When you reset the middle and grandparent generation to twenty, you interrupt that process. The middle generation is never going to inherit, and the young generation probably won't either, except for the last five years of their lives.
A large number of industries are going to run into a similar problem. With X number of commercial pilots flying, or X number of surgeons operating, and both will continue to work until they die of old age or get bored and find another career. Each industry has an educational pipeline to funnel enough new professionals into the field to replace the guys who leave the field. With ages reset to twenty, those pipelines are going to wither on the vine, simply because the need for new professionals has dropped to a fraction of a percent of the total workforce.
An expanding economy could fix some of this, but not all of it. When that age reset button is smashed, the economic fallout is going to be an earthquake in slow motion.
