Quote Originally Posted by Big D View Post
That flashback scene happens when Aerith is still very young, so it's possibly 20 years in the past. Biggs and Jessie don't look that old when Cloud's with them... sure, it's hard to judge ages accurately from super-deformed sprites with cubes for hands, but I'm reluctant to believe that those two are both in their forties yet are lacking grey hair or other stereotypically 'old' features.
Aeris is only 22, so it's unlikely it happened 20 years in the past, particularly when the incident with Sephiroth and Nibelheim was shortly after the end of the war. At most it might have been ten years earlier, which could put Biggs and Jessie in their mid-late teens at the very least if they were in their mid twenties when the game starts (not exactly a bad presumption since Cloud is 21, and we can assume Jessie is at least the same age.

That said, the game seems pretty inconsistent to me as far as the timeline of characters before, during, and after the war.