I have always wondered this because it states that they are twins or in some fanficitons, they are a year or a couple months apart. But I think I have a feeling that I know their age. If you subtract the first Night of the Living Dummy book by 2017 you get 24 (1993 - 2017 = 24). I know that I said in a previous post that I had always thought that Slappy was the oldest and Wally was the youngest. But I had a feeling that if you actually calculated their ages they would roughly be in their early-mid twenties. I also have a fanficition series called Goosebumps High, and I made Slappy 16 and Wally 14. But here is another fact, technically, Slappy and Wally were both apparently created in the 1800's. So say if you subtract 1800 by 2017 you will get 217 ( 1800 - 2017 = 217). But based on my exact research that I did, I would just guess thier age by the book's release date because I don't think that Stine had specifically stated when Slappy and Wally were created. And it says on the Goosebumps Movie's trivia section on the wiki that Slappy is the oldest out of all of the Goosebumps creatures. So that could also be a hint that Slappy is older then Wally. But right now, I would like to know your opinions down in the comments :) :) :) :) :) - Slappy'sGirlfriend2598.