When should you introduce a bit to a horse?

When is the appropriate time to introduce a bit to a horse? Should it be done early on in the training process, or is it better to wait until the horse has reached a certain level of obedience and familiarity with human interaction? Is there a specific age or developmental stage that horses should reach before being introduced to a bit? And how does the type of bit being used factor into the decision-making process? Additionally, what are the potential benefits and drawbacks of introducing a bit to a horse, and how can trainers ensure that the process is as smooth and stress-free as possible for both the horse and the rider?