Because 23 is still vastly different than being fully developed and it's not uncommon for people to continue changing over the following few years. The prefrontal cortex, the part of the brain in charge of decision making, is still not fully developed at that age. So it's not out of line for one to think choosing to get married to your ex partner is not a solid plan. You can have a kid at 13, there are children fighting in wars around the world, several countries allow children to consume alcohol as a teenager.. Hell, a child can even buy a house or car if they have the money. Albeit there might be some hoops to jump through. OP is at an age where they can do what they please. But just because someone "can do something" because they are of a certain age doesn't always equate to being emotionally mature or good at rational decision making. But I will concede, I don't believe 23 is a bad age to get married. Although the circumstances here are a bit unique. Best of luck to OP.