A few comments:

You can fly without Real ID, or without any ID for that matter, if the TSA is able to verify your identity and with additional screening. Last time I had to deal with it was before Real ID though when I lost my wallet. He should arrive early and tell TSA right away that he is not realID compliant. But... It could be a pain to and take long time if they are busy or possibly not work at all.

However, he should be able to apply for license from the DMV before then and possibly get it. The CA DMV allows you to upload all you documents in advance and then go to a office and without an appointment and check in at the appointment line (at least it did when I did it) as the confirmation email instructed:
You must bring the original or certified copy of the documents below to DMV. Please print or present this email or the confirmation page at the DMV for an express experience.
When you arrive, report to the appointment line at the Start Here window.

Even better though would be to get an appointment. They are definitely available (especially if he is willing to drive a bit) but the DMV website sucks and makes it super hard to do a broad search to find them. You can use this site to look for appointments and create alerts for cancellations.

https://dmvfilter.com

Though it will need to be right away as it will take 10 days or so to get the new license in the mail.