It is never stated how old Debbie is, but given that she's old enough to drive a car, she must be at least 16. Likewise, it is also never stated if she is in high school or college, but given that she was Max's babysitter way back when he was still in diapers, it is more plausible for her to now be in college. In the first place, in order for her to have been old enough to babysit Max as an infant, there would have to be a large enough age gap between her and the presently middle school-aged Max. As in, a gap larger than there would be if she, presently-speaking, were merely a high schooler. Therefore, if she is in college, then she would be at least 18 years old. Though she and Max are stated to be cousins, it is never explained how they are related. They are most likely first cousins, as Debbie consistently refers to Max's father as "Uncle Goofy," which in turn would mean that one of Debbie's parents is the sibling of either Goofy or Max's mother. Since Debbie is noticeably absent from Goofy's family reunion in "Calling All Goofs" (which both had the same writer as "Leader of the Pack" and was produced after it), this would suggest that she may be related to Max through his mother's side of the family. It is presumed that Max and Debbie hadn't seen each other since they were young children; upon first meeting her again in the episode, Max was quite surprised at how different she looked from the photo he had of her.