It is not permissible to tinker with the date that is recorded on the birth certificate for the purpose mentioned, because that involves deceit, lying and trickery in order to carry on working unlawfully.
If the employer stipulates that the worker should be less than 65 years old, then it is obligatory to adhere to this condition and it is haraam to use tricks to circumvent it. Similarly, if the workplace lets people go when they reach this age, it is essential to tell them and it is haraam to deceive them, because the Prophet (blessings and peace of Allaah be upon him) said: “The Muslims are bound by their conditions.” Narrated by Abu Dawood (3594), classed as saheeh by al-Albaani in Saheeh Abi Dawood.
And because of the general meaning of the evidence which shows that deceiving and lying are haraam.
And Allaah knows best.