Boarder income is generally not allowed. If your sone were to purchase a multifamily property and rent out the other units, then the income could be considered.
If your son is a full time student, you could be on the loan as a non owner occupied co-borrower. Your incoome, credit and assets could be factored into the qualifying.
You also could purchase the home as an investment property and lease it to your son and fellow students. Then you have nice asset to help you reduce your tax liability. Talk to your CPA about the joys of owning investment property.