Basically, if the child still needs it, it is too soon to give it up. There is no medical or psychological evidence that there is an age too old for comfort objects, eg Lovey's. Many children keep them until they make friends at school. Comfort objects are very important for children.
Teaching children to cope with stress will help with transitions. Even toddlers can be taught self calming, deep breathing, and excercise as forms of stress reduction. Once children can comfort themselves, they will not need comfort objects. It is very important to encourage healthy and safe methods of stress reduction. While there are countless examples of adults who engage in unhealthy comfort measures, such as alcohol or cigarettes, there are reports of healthy and normal adults who use comfort objects. https://en.wikipedia.org/wiki/Comfort_object
It is important for children to be able to express their worries to a confidant who does not judge them. For some children, comfort objects serve this purpose.
Comfort objects also help children cope with transitions and disappointments in life. Children used comfort objects for support and solace too.
It is important for parents to understand the role the comfort object plays in the child's life so that they can help the child make a smooth transition. If the child is comforted by the object, parents should provide the child with another source of comfort, such as a blanket, hugs, a shirt, or other object that the parents find suitable that the child finds comforting.
The best way to help a child leave the Lovey behind is to teach him or her to comfort herself or himself. Think about the healthy ways you calm yourself when you're stressed, and teach your child some of those ways. Some ideas: singing, yoga, deep breathing, talking to a trusted friend, running, dancing, stretching, a nap.
Threatening, bargaining, bribing, and shaming don't help children learn to sooth themselves. If the child doesn't say it's time, then it isn't time yet. There is so little in the world that children control, choose your battles. The comfort object means much more to the child than it does to the parent. Try giving comfort instead of taking it away.