Depends what you mean by holding back,just to let a dog sit in a kennel for 2 years wouldn't be much cop,or do you mean let it work the simpler places straight forward type earths just to build its confidence, some dogs do need the thinking done for them like, foxdropper says standards must be kept and waiting forever for a dog to start isn't good enough I like borders but I expect even a border to be entered and making progress by 2 years of age.