I could write a thesis on this, so I’m going to do my best to keep it pertinent to your question. I retired just over a year ago with 20.5 years of military service. Like your son, I am a pilot. I retired to pursue commercial flying (airline pilot).
Your basic mechanical understanding of the military retirement is correct, with the caveats already pointed out in posts prior. Bottom line from a monetary standpoint, my retirement pay is about 1/3 what I took home in the military because of BAH, BAS, and pilot bonuses which do not carry into retirement. If he is an O-5 with 20 years, he could retire right now at ~$50K per year. To contrast, he could retire at O-6 with 30 years at nearly $100K. Only your son would know if he has a reasonable shot at the advancement and his ability to stick around for a full 30yrs+
For me, and most others who make it to 20, retirement is not primarily a monetary issue. Does he like flying more than leadership? Does he truly believe in the jobs he is doing in the military? Is he happy with his duty stations and peers? What about family issues, like medical needs? Does he WANT to pursue flying as a second career, or does he want to stay in the defense industry or similar (contractor, GS, pentagon, etc.)? Personally, I was on the fence because I loved serving in the military (my childhood dream). I most liked the operational flying and team I worked with, but after O-5 (in the Navy), actual flying jobs are scarce. I wanted more than anything to stay in the plane, and my wife and kids wanted the final say on where we lived.
You seem to want him to be a commercial pilot. I get it (I am). Your neighbor’s pay and time-off is a possibility, but it is not as simple as it seems and sometime down the road in any case. If he is current, he MAY get hired by a legacy airline (about the only place your neighbor’s lifestyle is realistically available). If not, he will have to spend time getting current at smaller airlines. Life there is tough, work rules are abysmal, and pay is shit (can be close to the poverty line, depending). Then you get to your legacy airline. It is not a meritocracy there - it is seniority based. The longer a pilot is there, the better his pay and quality of life. First year pay can be eye-wateringly low depending on the airline. He will likely sit reserve for some time or fly the shit lines nobody else wants until he is senior enough to pass those on to someone else.
Finally, job security in the airlines is finicky. Right now, the airlines are hiring at a never-seen-before pace. They will do that until the day they furlough a quarter of their pilots. That might be 10 years from now, or it might be tomorrow. Massive layoffs have occurred in every decade (sometimes twice) since the 1970s. With a looming recession and economic uncertainty, he has likely already missed the best opportunity to get higher on the seniority lists. Of course, the boom could last longer. Who knows - FedEx and UPS are already slowing or stopping hiring. Coming from a job with a reliable, consistent check on the 1st and 15th is mental leap many are not comfortable with.
That said, I love flying commercially, but it is far less interesting than military flying. I don’t have to deal with any of the extra administrative crap that really started to take up most of my time later in my career. I miss the satisfaction of military missions, and especially working with my team (squadron, crew, co-pilot) to do some meaningful, important, cool stuff. Now, the most exciting part of my flight now is the approach and landing, which usually just an administrative formality in the context of a military mission.
All this to say the you son is not solving a mathematical equation. There are positives and negatives to every decision, and he must weigh what is the most important to him. You should know that he is in a great place with a solid foundation, and it is likely that any decision will have an acceptable outcome and should leave him financially comfortable.
If you (or he) have questions, I’d be happy to take some time to answer.
Your post is valuable to me. It helps me understand him. Thank you.