Three old Grandmas

Three old Grandmas were sitting on a bench outside a nursing home. About then an old Grandpa walked by, and one of the old Grandma's yelled out saying, "We bet we can tell exactly how old you are." The old man said, "There ain't no way you can guess it, you old fools." One of the old Grandma's said, "Sure we can! Just drop your pants and under shorts and we can tell your exact age." Embarrassed just a little, but anxious to prove they couldn't do it, he dropped his drawers. The Grandma's asked him to first turn around a couple of times and to jump up and down several times. Then they all piped up and said, "you're 87 years". The old man was impressed and asked, "how on earth did you guess my exact age?" The old ladies started laughing and said: "we were at your birthday yesterday!!!!"