To be eligible in your own right, you have to have paid into Social Security for a total of 40 quarters before becoming disabled. Given child labor laws, it's rare that you could accumulate enough quarters before age 26 or so.
The other way is to be eligible on a parent's social security, as a "disabled child", which is defined as someone who became disabled before age 22. If you suffered a permanent disability at age 21, and have a parent who paid enough into SS to be eligible, you can receive "child" benefits from their account even as an adult: https://www.ssa.gov/benefits/disability/qualify.html#anchor7
This leaves an unfortunate gap for people who genuinely become permanently disabled due to an accident or medical condition that happens around age 22-25, because they can't qualify through either route.
Looks like there are different rules for disability for young workers:
"To be eligible for disability benefits, you must meet a recent work test and a duration work test.
The number of credits necessary to meet the recent work test depends on your age. The rules are as follows:
Before age 24 - You may qualify if you have 6 credits earned in the 3-year period ending when your disability starts.
Age 24 to 31 – In general, you may qualify if you have credit for working half the time between age 21 and the time you become disabled. As a general example, if you become disabled at age 27, you would need 3 years of work (12 credits) out of the past 6 years (between ages 21 and 27).
Age 31 or older - In general, you must have at least 20 credits in the 10-year period immediately before you become disabled."
-- https://www.ssa.gov/benefits/retirement/planner/credits.html
The flip side is this person is hurting society significantly less than some committing crimes - even worse crimes that are sentenced to jail time (which is very expensive).
But is that one thing going to stop him from ever working/living a productive life?
If you lose disability by starting to work, suddenly life becomes a lot more expensive and you can't afford things.
The Welfare Gap is real.
As far as I can tell, he'll sit on his couch collecting disability until 65, at which point he'll switch to retirement.