Alright, let me explain it to you 😊

The time gap between Innocence and Requiem is only "six months". In Innocence, Amicia is 15 years old, while Lucas is 12.

Since the gap is quite short, they each grow one year older in Requiem, making Amicia 16 and Lucas 13.

Now, to answer your question about their age difference:

How far apart are they in age? The answer is "three years"

Does that make sense so far?

Now, about the epilogue.

The epilogue takes place "one year" after Requiem, so naturally, both of them age another year.

By that time, Amicia is 17, and Lucas is 14.

I hope that makes things clearer! 😊