also, generally speaking, junglers are those with some kind of passive lifesteal and/or extraordinary attack/defense combo who can drop the creep camps and keep fairly healthy while doing it. There's a way to do it with every champ, but it's pointless for most, and for some it damages their lategame build either by having a slow start or by having to purchase items that aren't part of their core build.

If you want to jungle at low levels, I suggest using warwick to get a feel for it. He barely needs runes/masteries to survive (they do go a long way, though) and his jungling builds directly into his role as lategame assassin anyways. There is little more annoying than a warwick with madred's bloodrazor and a guardian angel healing himself all the damn time.