There are number systems that allow operations on infinity.
You can of course make up a system in which by definition you make up numbers and, and make up operations and define them. You can make the system logically consistent. The names you give the numbers and operations can be the same as the operations used in the real world. However, this is basically circular reasoning and the results would not necessarily correspond or serve as a model for any thing that happens in the real world. If fact, pure mathematicians delight in coming up with math systems that have no practical value or relationship with the real world.
There are number systems that allow operations on infinity.
http://en.wikipedia.org/wiki/Surreal_number