Can I claim my Autistic 19 yr old son who has had no income or government assistance?

You can claim him as a dependent under the Qualifying Relative rules since he is age 19.

To be a Qualifying Relative -

1. The person cannot be your qualifying child or the qualifying child of any other taxpayer. A child is not the qualifying child of any other taxpayer if the child's parent (or any other person for whom the child is defined as a qualifying child) is not required to file an income tax return or files an income tax return only to get a refund on income tax withheld.
2. The person either (a) must be related to you or (b) must live with you all year as a member of your household.
3. The person's gross income for the year must be less than $5,050 (social security does not count) in 2024
4. You must provide more than half of the person's total support for the year.
5. The person must be a U.S. citizen or a U.S., Canada, or Mexico resident for some part of the year.
6. The person must not file a joint return with their spouse with the following exception -
You can claim a person as a dependent who files a joint return if that person and that person’s spouse file the joint return only to claim a refund of income tax withheld or estimated tax paid.

Perhaps.  A dependent must meet the requirements of a qualifying child or a qualifying relative in order for you to claim them on your tax return. 

The tests for a qualifying child are:

• Relationship: Must be your child, adopted child, foster child, brother or sister, or a descendant of one of these (grand or nephew).
• Residence: Must have the same residence for more than half the year.
• Age: Must be under age 19 or under 24 and a full-time student for at least 5 months. They can be any age if they are totally and permanently disabled.
• Support: The dependent must not have provided more than half of their own support during the year.
• Joint Support: The child cannot file a joint return for the year.

The tests for a qualifying relative are:

• Qualifying Child: They are not the “qualifying child” of another taxpayer or your “qualifying child.”
• Gross Income: The dependent being claimed earns less than $5,050 in 2024.
• Total Support: You provide more than half of the total support for the year.
• Member of Household or Relationship: The person (a friend, girlfriend, non-blood relative) must live with you all year as a member of your household or be related to you.

TurboTax software will ask you simple questions and give you the tax deductions and credits for which you are eligible based upon your answers.

See also these TurboTax Helps.

Who Can I Claim as a Tax Dependent?

Rules for Claiming a Dependent on Your Tax Return

You may also want to view IRS Publication 501. Dependents, Standard Deduction, and Filing Information page 11