I know this is subjective but usually at what stage or after how long of talking do you start to become exclusive with eachother? And how is that conversation even brought up?

This entirely depends on how committed the both of you are. You start the conversation simply by just bringing it up. If you want clarity then you should go for it, don’t waste time x

For me personally a couple months has been enough time for me to know if I want to be exclusive with someone. I think it's more about your goals of dating and how well you feel you know the person than a specific time frame. If you are dating to explore your options and see different people, or if you want time before committing, then you should take longer to become exclusive. But if you prefer to date only one person at a time, then it makes sense to become exclusive earlier. Just keep in mind that the other person may not necessarily have the same view as you as to when they want to be exclusive. To bring it up you can just say, hey I was wondering if you're seeing anyone else and how you feel about starting to date exclusively.