Yes, you can claim you son as a qualified child dependent as there is no age limit if he is permanently and totally disabled as long as he meets the requirements listed below:
For a Qualifying child
- They must be related to you.
- They can’t be claimed as a dependent by someone else.
- They must be a U.S. citizen, resident alien, national, or a Canadian or Mexican resident.
- If they are married, they can’t file a joint return with their spouse.
- They must be under the age of 19 (or 24 for full-time students).
- No age limit for permanently and totally disabled children.
- They must have lived with you for more than half the year (exceptions apply).
- They didn't provide more than half of their own support for the year.
You may be eligible for the following tax benefits if you claim your niece as your dependent.
- Head of Household filing status
- Earned Income Credit (EIC)
- Child and Dependent Care Credit
- Child Tax Credit
- Medical expense deduction
- Education Credits
For additional information, review the TurboTax article Rules for Claiming a Dependent on Your Tax Return.