State tax filing

There is no penalty for underpayment of federal income tax if you withhold or pay estimated tax at least equal to your previous year tax liability. Since your son had no return filed for the previous year his tax liability was zero and he will owe no tax penalty for whatever is income is for the next year.  He has to be sure to “tell “ the program that his peor tax liability was zero to avoid the program calculating a penalty on form 2210.