If he likes football, make it look like a football field.
Would Like Ideas For An 80 Birthday Cake For A Man.?
How about a cake in the shape of the number "80"?
You can either find out his interests and that will give you idea or maybe a photo of him when he was young hope this helps
You can have a cake that says like "big 80" on it and out 80 candles on it or whatever :D happy birthday to whomever this birthday is :D