(WXYZ) — Big Boy is turning 90 years old this month, and to celebrate, the iconic family dining chain will have special offers, memories and more. The chain was founded in 1936 and is still headquartered in Southfield. Monday, June 15 marks National Big Boy Day to celebrate the anniversary. On Monday, people can get the original Big Boy sandwich for just $1.90 with the purchase of a Pepsi product.