You can claim him as a qualifying relative dependent only if (a) you pay more than half his total support, and (b) his taxable income is less than $5050 for 2024.
The rules for qualifying child dependent get a little more complicated. You can claim him if (a) he lives in your home more than half the year, (b) he does not provide more than half his own support, and (c) he is disabled.
For this test, disabled means unable to perform gainful work (work for money). If he can work a part-time job for minimum wage or better without special accommodations, then he can do gainful work. However, work in a sheltered workshop for persons with disabilities is not gainful work even if he is paid. Because of the focus on gainful work, many people with medical disabilities are not disabled for tax purposes if they can work (amputees, blind or hearing impaired, etc.).
If he is considered totally and permanently disabled, then his age does not matter and neither does his income. He basically qualifies as a qualifying child as long as he does not provide over half of his own support and he lives with you for more than 6 months of the year.
If he is not totally and permanently disabled, then if he earned more than $5,050 you cannot claim him even if you provided all of his support for the year.