I concur from the human behavior POV that the recruiter was giving you the path of least resistance kind of answer-NO.
1. There is a waiver for many things and it would have taken real work to get a real answer that would "bind" the USMC
2. Given the likely timeline on said work plus your son's age (16.5), there would have likely been no career benefit to the USMC recruiter at all
3. This recruiter in this area may have so he simply does not have to work that hard to get his numbers. I know from the "news" the the Marines have hit their recruiting number over the past few years even when the other services have not.
Re the FBI agent route
"The only person I know who made it from undergrad to FBI was a woman who had a degree in forensic accounting who spoke absolutely fluent Farsi."
The only one I know of in 24 years as a federal prosecutor was a male who earned his BS/MS in Comp SCI in 5 years max from either Texas A & M or Tech and worked in the school's computer lab during the pendency of his application. He was assigned to a BTDT Agent for a couple of years of seasoning and now he is rumored to do some serious work in the cyber arena on a national/international level.
I have no doubt that your son with you as his father, coupled with his work ethic and accomplishments to date, will figure out a way from him to scratch his service itch.
EDITED to ADD: Re the Medical Field
Here in the KCMO area- they are paying 12, 000 hiring bonuses for nurses. I scouted with a kid (BA in Business for MU) who decided after 2 years of selling real estate with his father (top 5 agent in the metro) and his father surviving a serious head injury re a moto accident that he wanted to, at least initially, be a nurse.
Given the needs of the field in general and being a fit looking male, he has been told since day one that he will make the short list in any hiring situation right off the bat.
IF I had a child who excelled in STEM stuff, I certainly would steer to Pharmacy. Everybody loves them. Good money. Predictable hours. Solid working conditions. Highly portable.
I have often thought that a married/partnered set of Pharmacists could bet set for life by 50.
Presume a Combo BA/Pharm program that takes 6 years to complete. v. Med School (4 yrs BS + 8 yrs Med School)=8 yrs
In year 7 the Rx makes 125 k working 40-50 hrs a week/Med student makes =0
In year 8 the Rx makes 127k working 40-50 hrs a week/Med student makes =0
In year 9 the RX makes 130K ....................................../Newly minted Dr in residency makes 65K working 80 + hrs a week
In year 10 the Rx makes 133K..................................../.................................................. ......67K.....................................
In year 11 the Rx makes 135K.............................................. ................................................70 K.....................................
Finally after 3 years of residency, the Dr is making real money as a Family Practitioner-200K maybe? If the MD is going for a more specialized field, the residency could be 5 years with a fellowship year after such that it could be SIX years before they are making 350+
The Rx is about 400K ahead/gross all day long min. if there are two and the Dr is not married/partnered, the "Rx Family" is 800k ahead.
I digress as neither of my twins will be going down this route.