Let us consider.

Madara (who was roughly the same age as Harashima) had a pair of eyes. He then got his EMS eyes from his younger brother who died.

Now, Madara, an old as hell geezer living in a cave had given Nagato his Rinnegan eyes (that's practially another 2 kage in generations down to Hiruzen

& now finally 1 of them is in Obito's skull, where we're currently in the generation of the 5th Hokage.

So, how old can those eyes be? Considering Tsunade remembers her grandfather the 1st hokage it couldn't be that old right? Well considering that Tsunade is 50/60+...

Anyways, my point is that they should proooobably have rotted away at this point. But of course, the "Eternal" Mangekyou Sharingan...

So take a stab people, how old are those damn eyes?