For the sake of reference (and my own sanity)
In my fic, the boys are the following ages at the beginning
The Love(s) of a King:
Yuri: 19
Otabek: 20 (turns 21 during Chapter 6)
JJ: 22
Reasoning: The fic begins in 2019. In the series, Yuri is 15 during the GPF of 2015. He was born in March, and the GPF was in December. Therefore, he was born in 2000. At the time of the GPF, Otabek was 18, and his birthday is October 31. If he and Yuri had the same birthday, he’d be 17. That makes his birthday 1998. Because he hasn’t had the birthday in the fic yet, he starts at age 20. Same idea with JJ. In the series, he’s 19, but his birthday was before the GPF. Make his birthday the same as Yuri’s, and he’d be 18. This makes his birth year 1997. He’s already had his birthday in the fic, so he’s 22 at the beginning.
I Put A Spell on You (Because You’re Mine)—btw, you can casually refer to this fic as “Hocus Pocus,” because that’s what I do…
Otabek: 24 (turns 25 during Chapter 3)
JJ: 26
Yuri: 23
Reasoning: Otabek has been on his own for a decade. You learn later on that he lived with people until he was 14. The age gaps are the same as in canon, giving us the other ages.