Just noticed there are a couple of threads about dealing with squabbling siblings so will try to be brief.
DS1 is 3.1yo and DS2 10mo.
DS1 torments DS2 all the time. Can't pass him with out a 'pat' on the head, squeezing his thigh, a quick pinch here, a little push there, a 'hug' that leaves DS2 screaming and gasping for air. It's constant. Doesn't help that DS2 appears to have a low tolerance and sometimes just cries when DS1 gets too close.
I try to just remove one of them, ignore and distract but for the more serious (e.g a kick) I'll remove a toy from DS1 or turn TV off if it's on. I try to do an immediate consequence so he gets why I've done it etc.
It's not working though and I know that siblings will always squabble etc but DS2 is still so little. On some days I wonder if they'll ever get along? 
Was there an age when your kids just clicked and it got easier? Is it a case of waiting for the younger to get bigger and start giving as good as they get? How much do you ignore?