Your friend is at high risk due to his age and should wear a N95 in the proper manner if he attends.
Unless he has diminished mental capabilities (perhaps due to age) he should make up his own mind.
Even if you believe the anti-mask crowd regarding COVID your friend is at risk from every type of airborne illness that happens to be in circulation. Another poster suggested frequent hand washing and certainly he should not touch his face or eyes after handing firearms on display.