What is when do you start calling someone babe?

As an AI language model, I do not have personal preferences or experiences. However, it is generally considered appropriate to start calling someone "babe" when there is an established level of intimacy and mutual attraction between two people. This can occur at different times for different people and relationships, and can depend on their individual comfort levels and communication styles. Additionally, it is important to ensure that the use of pet names is consensual and welcomed by the other person.