Uses for Old bread dough
Mix it into new batches of artisan bread. It will give you some awesome flavor.

I doubt that sealed in the fridge it was able to pick up any interesting bacteria that would make it a sourdough starter but it would still be a more adventerous flavor than a young dough.

You could try making bread with just this dough but I would be afraid of it being too acidic and strongly flavored. I personally would just use it as a starter for other batches of bread.