How could Aang stay alive for 100 years? Is there any clear description as to how Aang survived for 100 years inside of the iceberg?

Can Avatars do that? If they can, then why didn't the other Avatars stay alive for long time periods? And whatever was the case, how did Aapa stay alive too?
From Avatar Wiki:


  However, Aang later discovered that he would be sent to the Eastern Air Temple in order to complete his airbending training far away from Monk Gyatso, whom the other monks thought was too soft on him. Afraid and confused, the young airbender ran away with his flying bison, Appa, though they became caught in a storm shortly after, which caused them to crash into the water. Aang saved himself and Appa from drowning by semi-consciously entering the Avatar State and freezing them both in a sphere of ice through a combination of airbending and waterbending. The Avatar State kept him alive, albeit not fully conscious, in the iceberg for about a hundred years while the war raged on.