Can I apply for my mom for Green Card ?

If your mom entered with a visa, then you, her US Citizen child over 21, can sponsor her for her green card. However, if mom did not enter legally, it's still possible to adjust her status but it's far more complicated. 

As long as you are at least 21 years of age and your mother entered the US with a visa or was paroled, you are able to apply for her and she is eligible for adjustment of status. If your mother did not come in with a visa or was paroled, she would only be eligible for adjustment of status if she is an applicant under §245(i) under which she would either have applied for immigrant visa petition or labor certification application by April 30, 2001, and have been present in the US on December 21, 2020. If your mother is not adjustable, you and she can explore the possibility of her eligibility under an I-601A waiver. Due to the limitations of the Lawyers.com Forums, Alan Lee & Arthur Lee, Esqs.’ (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.