Consider the AF Reserves or Air National Guard. 10 year commitment but it's a Reserve commitment, so you can presumably min run it or transfer with greater control than fulfilling an active duty service commitment. You may not build hours as fast as you could on a regional, but then again putzing around a grass field on a C-150 will prove more tactical and 'fun' than following a caret with the autopilot on in a tanker while catching up on your ancillary training (nothing to do with flying), which is all you'll be doing at the airlines anyways sans takeoff, approach and landing.
Being 21 you still have a ton of time to get picked up before the UPT cutoff of 30 years of age. I am still somewhat puzzled by your skepticism for the time commitment; you do realize it's the military and there's no free lunch right? I recommend the Reserve components only because they provide the closest to what I would construe as a 'homesteading option', which is the number one reason I pursued the Reserves, with the accompanying paycut, straight off college.
If I were you I would do a gut check as to how fulfilling you really think droning around in airliners is really going to be, with the accompanying life schedule, compared to the opportunity cost of being an accountant 9-5 and pursuing a hobby on your off time. I say this because I know too many a regional FO who went zero to hero and hate life now and all of a sudden they want the fast track into a Guard/Reserve job and they're coming up to the 30 yo age deadline lickity split.
Also bear in mind, if the degree was an issue for pursuing officer pilot positions in the other branches, you could still pursue the army helo pilot route on the army reserves (they're not much of a reserve though ops tempo wise, and you know exactly what I mean). But don't sell yourself short just because of a flawed perception of what satisfaction you may draw out of a particular set of hypotheticals. That is not an efficient way of spending your productive life. Living life constantly disavowing the notion of foresight for the educated fool mantra of "i can only know something after I've done it" can be quite expensive and non-reversible in a life that affords you no do-overs. Which is why I love these boards for the young guys, you get to see people's outcomes without having to expend your own human capital in the process. I can tell you the information I uncovered on these boards was instrumental in my determination to never pursue airline work. Of course that will be your own journey, to each their own. Good luck.