How old are these guys? Cuz a 15-year vet of the US forces could have been in Vietnam, the Dominican Republic, Lebanon (the first time) and still be only 33. On the Soviet side, yes, you're pretty much out of luck. Even the 1968 Czech intervention isn't so much "combat" as "target practice." But wasn't there a Sino-Soviet clash on the Ussuri River in '68 or '69? That, if I remember rightly, was real serious tank combat, which should count.
If only the aliens would land somewhere that we already had tanks sitting around ... we'd show 'em!