Tiger 1 from 1942 can face the Ratel from 1976, 34 years (it also means Tiger has to face MILAN ATGMs which is just ridiculous.
the biggest that hasn’t been mentioned that I can think of is maybe the Gloster Meteor (designed in 1943 and entered service in 1944) facing the F117 (1983) in an up-tier that’s 40 years