How can a pensioner give an apartment to his son?

The notary said incorrectly. The law does not prohibit the conclusion of a gift contract for pensioners.

Also, nothing prohibits concluding an inheritance contract. According to the inheritance contract, one party (acquirer) undertakes to comply with the instructions of the other party (alienator) and in the event of his death acquires the right of ownership of the property of the alienator (Article 1302 of the Civil Code of Ukraine).