Cat still greedy and selfish at 11 months!?

We got a kitten last august which was 6 weeks old. He was abused. Thrown from heights. Bad diet. Thrown around. He's really lovely and our older cat became his big bro in no time, but he is sooo greedy still. He scoffs food as quick as he can, we separate them as if we don't he gulps his down then steals our older cats. If treats r laid down he trys to get them all. He grabs food from peoples hands. How can we teach him? He eats in his own room at feeding time and is told NO firmly when he steals food. But hes nearly 1 and he hasn't changed!!