On that day, they'd walk across the lake to the boat club for their first legal drink.
So when Len's 21st birthday came around, he and his pal Corky took a boat out to the middle of the lake. Len stepped out of the boat and nearly drowned! Corky just managed to pull him to safety. Furious and confused, Len went to see his grandmother.
"Grandma, it's my 21st birthday, so why can't I walk across the lake like my father, his father, and his father before him?" Granny looked into Len's eyes and said, "Because, ya dumb arse, yur faudder, grandfaudder and great grandfaudder wuz born in January, you wuz born in July."