It depends. You can include medical expenses you paid for your dependent. For you to include these expenses, the person must have been your dependent either at the time the medical services were provided or at the time you paid the expenses.

If the expenses were paid or services were provided when your son was your dependent, then the answer is yes.

However, if the payments or services occur during a period where your son is not your dependent then the answer is no.

For more information about deductible medical expenses click here.

However, there is such a thing as a Medical Dependent, who is an individual you would have been allowed to claim as a dependent except one of these applied:

• He or she received gross income of $4,300 or more in the year.
• He or she filed a joint return for the year.
• You (or your spouse if married filing jointly) could be claimed as a dependent on someone else’s return in the current year.

2020 Publication 502 (irs.gov) at page 3 ("Dependents").