I've had cream ales that I had had in the bottle for a year and they still taste good. As long as your storage area is dark so the beer doesn't get skunked your stout should be fine.
The exception I have found with longer storage is with my pale ales where the hop aroma fades with time. The one I bottled in November had aroma that just popped when it was young but now it has faded. It still tastes good, just not the aroma it had.
If you have a place to keep the bottles cool, it should be just fine. I have a coffee stout that I drink a few bottles each year that started out 4 years ago, and some Christmas ales (stout base) that are even older.