I'm 54, female
I have a son that is mildy retared and gets SSI check each mo. He is 19 and does not work.
He lives with me.

You should file Head of Household and claim your son as a dependent.

You will NOT get the Child Tax Credit due to his age.

However, the fact that he gets SSI would indicate that he is considered totally disabled. If so, that would allow you to qualify for the Earned Income Credit if your income is less than $33,241.