I paid childcare for my 19yo disabled son. I cannot get him listed for childcare expenses (he doesn't appear as a possibility because he is 19yo). How do I list him?

You can claim a Dependent Care Credit for children 13 and over, such as your 19 year old son, in certain situations. ‌The child must be considered "disabled."  

To be considered disabled, both of the following must be true per the IRS: 

1. "You can’t engage in any substantial gainful activity because of a physical or mental condition.
2. A qualified physician determines that the condition has lasted or can be expected to last continuously for at least a year or can be expected to result in death."

Here is how to claim the credit in TurboTax Online:

• First, navigate to My Info > Your Household > Name of the child > select to expand menu, choose edit
• Continue until you reach "Less common situations for child"
• Select "Was disabled"
• Next, navigate to Federal > Deductions & Credits > Dependent Care Credit > Add/Edit
• You will then enter the cost of care for the period of time the child was considered disabled