Is it too late to enlist in the Illinois National Guard at 43?

SPC Victor Doydora Most services will subtract your years of service from your age. So, if you're 42, and had 6 years in, your age (according to them for reenlistment) would be 36. So, you would need to see what their limits are. In MO, Army Guard was 36, but Air Guard is 40.

No. But you better get cracking. I still believe the door closes at 45 yoa.

i was 10 years active duty with the Navy, then joined the Guard. At 51yo, my AD time was subtracted from my age. At the time, 45 was the cutoff age for prior military. Verify the current requirements with a Guard recruiter.