I grew Aji Rosita and Aji Margariteno from 2015 seeds last year. I was pleasantly surprised when I got 12/12 germination on those 8 year old seeds. In fact, the Aji Rositas were the very first variety of my 2023 season to pop (in only 6 days). And all 12 of the old seeds had germinated by day 16. I did keep those seeds stored in ziploc baggies in the fridge for a good part of those 8 years. That may have helped my results, but I can't know that for sure. Anyway, I think those are the oldest pepper seeds that I have tried to germinate so far.