Well, its possible Isshin and Masaki as well as many other characters we dont know their ages for to be well over a 100years old at the very least. Take Rukia for instance, she is well over 100 years old (even stated so in the first dozen chapters and episodes of the anime) and she looks not much older than 15-20 compared to other characters. So lets say they all age the same and at the same rate (with exception of Yamamoto the Captain Commander). given Isshin and Masaki's looks they should be around 300-400 years old. So i would say that incident appearing in the manga right now with Isshin, the Black Hollow, Aizen and Masaki would be a possible 20-100 years ago. Isshin looks like he is definitly at least 20 years younger than he does current time, same with Ryuken.
But a bit more on topic with how Bleach's time works in their realities. I think its possible that time may be slower in the real world of humans, rolls by 10x fast (or faster) in Soul Society (Which could be why they dont age much...) and when they train in the Dangai using that Technique Isshin and Ichigo used, they slowed time within time in a 4th dimension to train for 1 year.
But alas at this time its hard to tell how time is perceived.
