Where do you get a old rod on Pokemon Platinum?

To acquire the Old Rod in Pokemon Platinum, you must first go to Jubilife City. Upon entering the city, go a little north and then walk west until you enter a walkway in between Jubilife City and Route 218. Inside the house will be a fisherman and a guard. Talk to the fisherman, and then affirm that fishing is good. He will then give you the Old Rod.