I must agree with you.
Their question(s) in Matthew 24:3 were based on His PREVIOUS talk with them in Matthew 13:24,39,40,49-50 (re: 'the end [singular] of the age [singular]')
and what He'd said just before this, in Matthew 12:32 (re: 'the age [singular] to come') which I believe they
correctly understood
that (Matt12:32) to be referring to what we NOW/CURRENTLY/commonly call "the promised and prophesied earthly Millennial Kingdom" (i.e. His "reign" [in power]). Sure, they didn't grasp He was going to "die" first, before getting there to that [future] point, but in their minds,
"thy coming" [as I see it] meant
His coming into His "[earthly] REIGN" (just as had been prophesied).
Their expectation was correct, they just did not understand its TIMING,
or what events had to take place in the interim (His death and resurrection / exaltation, etc). It kind of reminds me of how one of the high-up dudes, during Jesus' trials,
inadvertently "prophesied TRUTH" in what they'd said (I forget which one, and the details there, though I've posted about it in past posts
[it's way past my meal-time and the brain-sludge has kicked in...
])