I'm a big college advocate for professional pilots, for several reasons, but in this exact moment it would probably make sense to do the crash course, get to a regional and start building time/seniority so as to catch some of the wave. Unprecedented opportunity. I would encourage him to keep chipping away at the degree, just in case.

Or compromise and do the associates degree route for two years, hustle for flight time in the process and get on with a regional at age 21.

Keep in mind that the R-ATP requires age 21, so he can't start a regional before that. If he really hustled he might be able to get a 91/135 turbine job before age 21, and then go directly to a major of some sort when he's 23 with a few thousand hours. Lots of potential paths right now.