What type of earnings?

W2 earnings. 

Not a dependent.

kudos!!!

You betcha!

Who paid for over half of the son's support?

Depending on the circumstances, the parents MIGHT be able to claim him as a Qualifying Child.

You'll need to determine if he meets the tax definition of "permanently and totally disabled" (see first link).

And $17,000 could be under the "substantial gainful activity" .

https://www.irs.gov/publications/p501#en_US_2024_publink1000220897

https://www.ssa.gov/oact/cola/sga.html

I think we're on a border somewhere (but I'm not sure which side of it).  Obviously we don't have all of the facts but it sounds like all of the other requirements are met for a QC dependent.  If you run through the ITA looks like he qualifies.

The question in my mind aligns with Bill's thinking here.  Since the post mentions disabled I'll assume that condition has been met (I'm under the impression it's not too hard to get a doctor to sign off on these things).  So that leaves us with the mystery of "substantial gainful activity".  I couldn't find an IRS "bright line" for this but did find the same thing that TGB found on ssa.gov, with $17K slightly under 12x the monthly amount for 2024.