Does the ruling of an oath apply to one's age, knowing that the lie in court was made before the judge requested the oath, and the age is irrelevant to the case?

What happened from you is an incorrect statement about your age, which is a lie and has no relation to your oath. You did not swear an oath regarding that, and therefore an expiation for an oath is not binding upon you. However, you must repent to Allah Almighty for lying.