My Ds was 3 when we encouraged him to part with them. He wanted a party on a train for his birthday so we told him he could but big boys who have parties on trains don't have dummies so he would need to give his to the train driver for the babies. This worked for us because DS is train mad and he really wanted that party!!!!!
I am not sure I could take the dummies away at 8 months if they were relied upon for comfort. I have read that some babies/infants have the sucking reflex til they are 3 and I am sorry but I am a bit of a 'anything for a quiet life' kind of parent within reason