Ash's Pikachu

I have discovered when Pikachu will evolve. After a great deal of consideration I discovered that he will evolve when Ash becomes eleven years old. Think about it people ...

Pikachu won't evolve. It doesn't want to evolve and Ash respects that. Also, there was a small case in Unova that touched on that when Ash needed to find a Thunder Stone during the scavenger hunt. When the guy tossed the Thunder Stone it was heading right toward Pikachu but Ash caught it before it touched his yellow companion.

Pikachu's reaction when it was flying at him? Wide eyed because it didn't want it to happen.
After Ash caught it? Both of them were relieved.

That's all there is pretty much to it. But I might be one of the very few who don't mind Pikachu staying as a Pikachu. Raichu, who is a little slow and bigger than Pikachu, wouldn't match Ash's battling style which likely developed because Pikachu was his first Pokemon.