I don’t actually know her age, but just from her behavior I can confidently say she’s not mature enough to be in this relationship.
Anyone dating a single parent immediately has to reconcile that 1) they are not automatically the kid’s parent because they’re the parent’s partner and 2) there is a high likelihood the parent will have a complex relationship with another person. If you want someone who only has you in their heart, do not date a single parent.
And what does this girl do? The moment she gets a nuanced answer from the MC? She immediately takes it as a yes and takes it to its most extreme, using public pressure to force him into the relationship she wants. The irony is by doing this, she confirms that the MC is right: she’s too young and not ready to date a middle-aged man with history and baggage.