The hot new video sharing app isn’t just teenagers producing memes and miming along to their favorite pop songs — Among the teens creating TikTok videos about the undeniable, bone level differences between freshmen and sophomores, you can find Jenny and Mike Krupa, both 88-years-old, explaining the perks of being octogenarians. Though the senior citizens’ account (@its_j_dog) is run and scripted by their 19-year-old grandson Skylar (“I knew people really…