If it were sufficiently large to reflect enough light for us to recieve and see, we would probanly not see an image, but a ten year old point light source. No discernable image.

What ever is behind it.

Depends. Where is the source of light? If it is the sun, it would take the same time for the sun light to travel back and forth as our reflection. If the source of the light is much closer to the mirror, we won't be able to see anything BUT the source of light and our reflection would be washed out by that light.

For light from our solar system to reach the mirror would take ten years. It would take another ten years for the light to be reflected back.

You would see 20 years into the past. 10 years per direction that the lite travels.

Oh stop that, my head will pop

Some people seriously have way too much time on their hands...lol

How about this? We need to get up each morning, stand naked in front of the mirror, and then decide whether we should eat eggs and toast or skip a meal that day...much more "down to earth"...ha ha ha