The first type of dependent is a Qualifying Child. If someone does not fit the bill, there is still the possibility of being a Qualifying Relative.

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 2019 taxes as long as they meet all of the following requirements :

@Rubyq310

• You provided more than half of their financial support. More info
• They made less than $4,200 in gross income during 2019 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.

Your answer did not provide any age restriction. My daughter is 25. Made less than $4300. She lived at home. And I provided more than half of her support last year. My refund got adjusted because they said I made a mistake with one of my dependants because of age.

A child that was 25 as of 12/31/20 only qualifies you for the $500 Other Dependent tax credit.   That child could not qualify you for the Earned Income Credit or the Child Tax Credit.  Even as a full-time student, children 17 and over do not qualify for the Child Tax Credit.   They may be referring to the age of another dependent on your return.   Did you have a child born in 2020?   If so, be sure to indicate that the child lived with you for the WHOLE year.   

There is no age limit for claiming a dependent as a qualifying relative as is the case with your 25 year old daughter.   If she made less than $4300 and you provided more than half of her support, you can claim her as a qualifying relative and claim the $500 credit, but not the $2000 credit.   

@kaely123