In the far off future of Dextopia, Old Man Dexter spends his time as the wise ruler of the world sleeping on his rocking chair while still living with his big sister Dee Dee. Dee Dee continues to pester Dexter even in their golden years and Dexter still maintains his "sister alert" warning system. During one of their interactions, they spent their time telling stories of their youth (although poorly remembered) with Dee Dee occasionally correcting or worsening Dexter's memory. In the end, Dexter grew too tired and fell asleep and his still loving sister put him to sleep on his rocking chair and gave him a blanket before leaving the room.
Old Gal Dee Dee (along with Old Man Dexter) makes a cameo appearance in the season 2 episode Unfortunate Cookie where Dexter imagines himself stuck with Dee Dee forever if the Chinese finger trap couldn't be removed. Interestingly, Old Gal Dee Dee's appearance in Dexter's visualization appears to be a lot different from Bygone Errors: in this episode Old Gal Dee Dee is as tall as her child counterpart, has two curled buns similar to the ponytails she had when she was younger, still wears the same clothes as she wore during her childhood, and uses the aid of a walking stick rather than a walking frame.