The maximum allowed age for enlisting in the Navy is 34.
The Air Force allows up to 39 and the Army is 35.
This is not applicable to those like myself who are prior enlisted Mustang officers.
There is a specific policy that allows reversion to an enlisted rank of equivalent TIS, etc. that you had at your offer rank if you are between 16 and 18 years when you are 2XFOS to still be able to retire. All of the policies i've seen continue to state active duty or active federal service and it remains unclear how this impacts officers already in the reserves when they are 2XFOS.
"WHAT IF I AM A LT OR LCDR (WHO WAS PRIOR ENLISTED) IN A GROUP
THAT IS NOT OFFERED CONTINUATION, BUT I HAVE BETWEEN 16 - 18 YEARS
OF SERVICE AND STILL WANT TO RETIRE FROM ACTIVE DUTY?
Contact the Officer Favorable Resignations/Separations Branch (PERS-834F) at COM
901-874-2085/2095 or DSN 882-2085/2095 for more information on the option to
revert to an enlisted status."
http://www.vr61.navy.mil/bupers-npc...ed Questions About Continuation and 2XFOS.pdf
"Resign and Re-Enlist iaw CNO Policy Memo
Active duty Lieutenant and Lieutenant Junior Grade officers with prior enlisted service that have twice failed of selection for promotion to Lieutenant Commander or Lieutenant may be eligible to resign and re-enlist (informally called "reversion") in order to reach retirement eligibility. These officers must have at least 16 years, but less than 18 years of active military service on the date they would be separated, to be eligible for reversion. For further information on eligibility requirements for officer reversion please read the CNO Policy Memo from Dec 1990. To verify your eligibility contact PERS-834F, Officer Separations, at (901) 874-2085/2095."
http://www.public.navy.mil/bupers-npc/boards/generalboardinfo/pages/statusnonselect.aspx
The key word here in Navy PERS lingo is "reversion" which means reverting from officer to enlisted. I've found policies indicating that if you were prior enlisted, you will likely revert to an E-6 and be allowed to retire, unless you were E-7 or above at time of commission then you'll be able to revert to that rank.
While the National Guard, etc. seem to be options for officers who are 2XFOS with above 16+ years, it is apparent that without a break in service we can simply just revert to being a Navy E-6 and still retire, at least from the research i've done in the last 24 hours of pouring over Navy regs, policies, and federal laws.
In terms of sanctuary at 18 years, according to federal law, it appears that O3's are also entitled to sancturary at 18 years and not just O4s:
"officers in the grades of Lieutenant Commander
and below who have not been selected for promotion 2 or more times, and are within two years of qualifying for retirement on the first day of the seventh month following approval of a promotion board's results, will be retained until retirement eligible per 10 U.S.C. § 632 : US Code - Section 632. This circumstance is informally known as "sanctuary."
http://www.public.navy.mil/bupers-npc/boards/generalboardinfo/pages/statusnonselect.aspx
....So based on all of this, it does seem that retirement is almost guaranteed even if I 2XFOS -- the question is just a matter of if I can reach sancturary as an O3-E at 18 years or get 2XFOS'd at 17 years and "revert" to an E-6 and just retire that way.
I'll call PERS on Monday to get clarification of all this and will report back what they said.