If you are the sole person responsible for a disabled adult can you declare him on your income tax as a dependent if he is 27 years old?

You can only do this when you and this disabled adult meet all of the necessary rules that have to met for you to be able to claim this disabled adult as your qualifying relative dependent on your 1040 income tax return.

For all of the rules go to the IRS.gov web site and use the search box for PUBLICATION 17 go to chapter 3