The following two factors mainly determine if a topic is too broad:
You find too many sources - more than you can practically look through.
You're trying to address too many research questions and objectives, or your questions are too open. A topic is too narrow if there is little to nothing written about the topic. Lastly, you should be able to clearly define the scope of your study to avoid choosing a topic that is too narrow or too broad. If you find that you are having to cover too many theories and concepts, it may mean that you need to narrow your topic.