The chart shows $185,000 - $537,560 for Americans ages 55-64 and $200,000 - $609,230 for Americans ages 65-74. That's in no way, shape, or form "very little" as you claimed.
$130,000 for Americans in their 30s isn't "very little" either. It takes time in the market for compound interest to produce wealth.
Your original post said nothing about retirement, but the article you posted as your source does. How much is enough for retirement depends on so many variables: Do they also have a pension, an annuity, rental income, social security, what's their lifestyle like, what are their annual expenses, do they live in a low-cost of living area, etc., but that's not the point here.
The point is you claim "most" of those stock holders own "very little", but I'm not seeing that from your source.
You have an over optimistic view of American finances. Most are a couple of paychecks away from disaster. Don't forget average debt:
https://www.experian.com/blogs/ask-experian/average-american-debt-by-age/
