My son (19) wants to buy his 1st rifle. He has a drivers license with our old address from 2yrs ago. the dmv has the updated address on file.
Can he buy a gun showing the old info or does he need to get a current address license (and then wait the 30 days) to buy?
He doesn't have a car registration or any bills in his name with the current address either

Needs the current address +30 days

According to the ATF...

The identification document presented by the transferee must have a photograph of the transferee, as well as the transferee’s name, residence address, and date of birth. The identification document must also be valid (e.g., unexpired) and have been issued by a governmental entity for the purpose of identification of individuals. An example of an acceptable identification document is a current driver’s license.

A combination of government issued documents may be used to meet the requirements of an identification document. For example, a passport which contains the name, date of birth, and photograph of the holder may be combined with a voter or vehicle registration card containing the residence address of the transferee in order to comply with the identification document requirements. A passport issued by a foreign government is also acceptable so long as it has all of the required information.

https://www.atf.gov/firearms/qa/what-form-identification-must-licensee-obtain-transferee-firearm

Not quite right. If the license shows that it is a reissue, it's good from day one.
Also, if the DMV has been advised of the address change and has it in their
records, the buyer can usually bring it up on their phone or on the dealer's
computer.
Lastly, if the change was made in person at the DMV, they'll issue a paper
address change. That will work just fine.

does he have a DMVnow account?  as in can he pull up his DL on DMV website to show his current address?

if so, that is all he needs

or ,

is he registered to vote?    the dealer,  or he,  can pull up his voter registration with the current address,

May be a little past the threads prime, but I had this issue a few months back. The FFL (and other FFLs) accepted a hunting license showing my new address on it. There's a duck hunting HIP registration that you can get for free that will produce a license with your user imputed address on it that suffices.