Could the cranky kong from Donkey Kong country returns now be an elderly Donkey Kong jr?

Yes. "Cranky Kong" is Donkey Kong from the original Donkey Kong arcade game, in which Mario was known as Jumpman, and he was on an endless quest to rescue Pauline. It has been referenced since the original Donkey Kong Country game that "Cranky Kong" is in fact the original Donkey Kong, if you pay attention. For instance, when the game is first loading up and showing the developer splash logo, it shows "Cranky Kong" on the top of the last level of the Donkey Kong arcade game cranking a phonograph (a really old record player). He also refers to "his past adventures" when he was DK's age.