Hello, my son is 18 years old and just landed a job paying him $13 an hour. Is he exempt or not. I will file for him as a dependent in 2025. He will work May to August

No he is not exempt.  He might owe tax on his income if he makes over 14,600 in 2024.  

He is not exempt from being subject to income tax.  Whether or not he will need to file a return for 2024 will depend on his earnings for the whole year.  

@zwalochi 

No one is exempt from withholding, except maybe for foreign employee of the United Nations and other people with special legal status.  The withholding system is self-adjusting and proportional.  If we start with a basic personal exemption of $14,000, or $269 per week, he would only have taxes withheld if his weekly wage is more than $269.