J.M.
Let him keep sucking his thumb for now. He's just a baby and needs the comfort. My daughter is five and we "cut her off" at her 5th birthday. She wasn't psyched about it, but now has a loose tooth and knows she can't suck her thumb or it will mess up her "princess teeth." My son is 2.5 and is still a thumb sucker. We'll probably stop him at 5 too. Seriously, if he'll 11 months and can self-soothe with the thumb, stick with it for now.