I want to ask if I can put to my grandfather in my taxes because he is retiree.

If he has gross income of $4,700 or more in 2023 (Social Security does not count) then you cannot claim him as your dependent.

We do not have enough information.   Are you providing over half the support for your grandfather?    Does he live with you--or does he live somewhere else?    Does he have more than $4700 of income from any source except Social Security?  You say he has a "retirement plan."   If he has more than $4700 of income from that plan then you cannot claim him as a dependent.