You probably don't want to start until you're in the 20s, since your teammates will suck and not understand the logic of jungling until around that level. Even then you will probably get berated a lot. I didn't start jungling till I was level 30 personally, and only when I was certain we had a strong 1v2 lane (Morgana / Nasus / etc). The whole purpose of jungling is to provide an advantage to your team, after all - it wouldn't be good if your team wasn't skilled enough to take that advantage.
So i tried to jungle without smite with shaco at like..level 15 summoner. it REALLy didn't work. hitting 30 helped. Having all your runes, and the extra health from your quints, etc. But tbh, if I knew then what I know NOW...I would've just taken smite to jungle. since before you can have tier 3 runes, jungling is tough without it. Unless you're ww, which you should just take smite to make it faster. I would say, amumu, warwick, MAYBE Xin Zhao(never jungle with him..I always just lane cuz I get so many friggin kills, then turn into an assassin and I'm running around ganking lanes) and probably Udyr. I'm sure there are others, but normally i don't jungle anyway. If I Shaco, I just grab blue buff set a trap and have my lanemate lure them into it. instant double kill. lol. but yeah..Warwick is probably your best bet.
His health gets to a certain point and the combination of his passive and his w leads to him staying at the same health constantly, doing MASSIVE damage in there.
I did a match where I cleared out both jungles (I started at their golem and worked around) before mid hit level 6. --- Voltron had cats for arms. So when he punched you, you got mauled by cats. - Cereburus Q Rhaeme made me lol irl --- lalak