Humans start to pass it at around 18 months. My cat attacks his image, my dog licks it, and there you have it. :)

The other animals that pass it are:Asian elephants, Bottlenose dolphins, Great Apes, Orca whales, Eurasian magpies, and...ants.

"The mirror test was developed by psychologist Gordon Gallup Jr.1 in 1970 as a method for determining whether a non-human animal has the ability of self-recognition. It’s also known as the “mark test” or “mirror self-recognition test” (MSR).When conducting the mirror test, scientists place a visual marking on an animal’s body, usually with scentless paints, dyes, or stickers. They then observe what happens when the marked animal is placed in front of a mirror. The researchers compare the animal’s reaction to other times when the animal saw itself in the mirror without any markings on its body.Animals that pass the mirror test will typically adjust their positions so that they can get a better look at the new mark on their body, and may even touch it or try to remove it. They usually pay much more attention to the part of their body that bears a new marking.Even if an animal doesn’t pass the test, they may still have interesting reactions to their reflections.Many species respond aggressively, or even show affectionate behavior. In such cases, it might be that the animal mistakes its reflection for another of its kind. This can lead to some amusing sights for human observers.