If they get married, they would have to work pretty fast on making babies because at 40-42 years old there is about 35% miscarriage rate, and older than 42 years old, about 50% miscarriage rate.
If they turn out to be together (pretty obvious honestly) can it be at least a slowish burn? Like prolong it to when the guy physically becomes an adult again.
On one hand, a bittersweet story about a reunion of star-crossed lovers.
On the other hand, MC is 13 and the teacher is like 35, which makes for a very weird pairing.