dd just gave hers to santa last xmas, aged 3 years 11 months. she got a doll's house in exchange and is happy with that. she was given it as a newborn as she was incredibly sucky and had reflux and colic so it was imo necessary for all our sakes
ds1 is 2.9 and still has his although i've taken to hiding it during the day (because he keeps losing them outisde rather than any other reason really!) he'll give his to santa next xmas. he was also quite a sucky baby and with a close gap in ages between him and dd there were lots of times i simply couldn't feed for hours on end for comfort so gave the dummy at 5 weeks and he loved it from day one.
ds2 is 2 months and hasn't really taken to his dummy the way the other 2 did and i'm delighted about that but still have dummies to give him while he's awake if he's cross and i can't feed or he's fed too much and is sicking up but is still sucky, like i said though he's not overly interested.