Physical and Mental Development A 10- to 12-year-old dog, depending on his size and individual variation, is roughly the equivalent of a 60- to 90-year-old person. Answered By: Monty McDermott. Date created: Fri, Jun 4, 2021 10:21 PM. Age of Dog (dog's age according to the calendar)Dog's Age in Human Years (dog's age in equivalent human years, based on stage of breed size); Small Large; 12: 64: 77: 13: 68: 82: 14: 72: 88 Answered By: Newell Wolff ...