O am including two different statuses under which he may be considered a dependent. The first, due to his age, depends on whether or not he was a full time student. The second, assuming he won't be considered a child, mostly depends on his income.
Qualifying Child
Relationship — the taxpayer’s child or
stepchild (whether by blood or adoption), foster child, sibling or
step-sibling, or a descendant of one of these.
Residence — has the same principal residence as
the taxpayer for more than half the tax year. Exceptions apply, in certain
cases, for children of divorced or separated parents, kidnapped children,
temporary absences, and for children who were born or died during the year.
Age — must be under the age of 19 at the end of
the tax year, or under the age of 24 if a full-time student for at least five
months of the year, or be permanently and totally disabled at any time during
the year.
Support — did not provide more than one-half of
his/her own support for the year.
Qualifying Relative
You can claim a child,
relative, friend, fiancé (etc.) as a dependent on your 2018 taxes as long as
they meet all of the following requirements :
- You
provided more than half of their financial support. More info
-
They made
less than $4,150 in gross income during 2018 unless they are a qualifying
child.
- They
live with you or they are related to you. (Your relative must live at your
residence all year or be on the list of “relatives
who do not live with you” in Publication
501.)
- They are a
U.S. citizen, resident alien, national, or a Canadian or Mexican resident.
- They
aren't (or won't be) claimed as a dependent by someone else.
- They
aren’t filing a joint return with their spouse.
- You are
not being claimed as a dependent on someone else's return.
