How old is to old for a bottle ?

Michelle • 33 year old from Australia , currently pregnant with baby #4 a boy..miss 7 mr 5 miss 1 and prince due 26/01/17
So my neice just turned 4 and is still having a bottle before bed , does that seem to old ? I mean a cup of milk ok but not laying down with an actual baby bottle ! Idk am I being silly ? I have told my sister she needs to stop the bottle but she says she is still her little baby so will keep giving it to her ?