Does age matter

Two children aged 5.5 and 6 years talking about getting married to each other. They are planning to settle in USA. They are Ok if their parents are not there.I found this cute. Thinking how I would react/respond if these children were 12 years and above.Would I have just listened to them. Would I have given yhem some gyan for them or would I have trusted that they believe in the concept”am able.