Is it permissible to receive a salary from a job whose contract requires the age to be 18 years or older, when the actual age is less, and the age will be falsified in the documents?

Changing official documents, such as age or other details, is a forbidden act of lying and forgery. It is not obligatory to obey one's father in this matter, because obedience is due in what is right, not in what is wrong. As for the salary, there is no blame upon you concerning it if you are qualified for the job and perform your work in it perfectly.