You Take Each Other into Consideration
When you and your partner often use the word "we" when discussing future plans, you can consider it as a code to become exclusive. For example, "We’ll settle down here". Consequently, you should be aware of this code because maybe a close bond has already been built between you two. But if you find that your partner or both of you are taking matters into your own hands and not considering each other, no matter how many dates you have, then it's not the right time.
Your Chats Are Getting Deeper
In the early days of your relationship, you might talk about TV shows, gossip, movies, and sports, etc. And if at some point, you realize that what you are discussing is getting deeper and you care more about the inner thoughts of each other, then you can consider the exclusivity of this relationship. For instance, you start talking about your childhood, family, hopes and dreams, etc. In a word, your communication rather than the number of your dates plays a crucial role in a serious relationship.
Discuss a Serious Relationship
It's important to confirm that the person you're dating is interested in exclusivity instead of figuring out the number of dates you should have before deciding to go steady with him/her. People who say they don't know what they want or are still recovering from previous breakups should give you the hint they aren't ready to commit, no matter how many dates you have had together. When you determine to take your relationship to the next level, it is necessary to have a serious talk.