[Heidi n Q]

I have seen it in orphaned kittens and young-ish cats around the age of yours. Generally they do grow out of it. Sometimes they don't and you wind up with a "comfort-nurser". I had one who liked to suck thumbs. Specifically *my* thumb and I learned to sleep with my hands covered or under me. If I didn't, it was highly probable that when I woke he'd be attached to my poor, sore, thumb. He retained this behavior all his 11 years though after the age of 1 he really only insisted on sucking my thumb if he was feeling nervous; like when visitors first arrived.