This.... seemed a simple question for me to answer at first, until I remembered we had time shenanigans going on that I have to address haha! This also serves as an unofficial reveal of our new trainers. (more info under the cut!)
My sis and I grew up loving stuff that had messy but fun time stuff (most influential one being Zero Escape), so to bring these people together in a way that sorta make sense, we tried to make use of Hoopa’s abilities introduced in ORAS.
This is why I had to bring up exactly how we played the games, and the working timeline that is perceived by the trainers in their own flow of time!
They themselves acknowledge this too, and they always make sure to keep track of the correct flow of time and space, hence two timelines are observed in our verse: 1) the “in-universe” timeline (how they perceive time as above), and 2) the “real-time” timeline, the one that actually follows the games.
(Note: Pokemas seems to be using the same logic with bringing everyone together despite time discrepancies, but note that it came out last year, we thought of this concept first in 2016 so they copied us HAHAJK)
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Ages when they started in-game:
Roy/Gwen: 11
Alex/Ellen: 11
Basil/Ceci/Tim (GS Gold): 17
Julian/Maya: 12
Oliver: 10
Ophelia: 11
James/White/Kyouji/Mei: 16
Xavier: 17
Yvonne: 16 (some time after XY passed when she joined)
Louis/Lewis/Kiana/Dani: 11
Arthur/Emi (Galarians): 14
In "real-time" age, if we use SM/USUM as landmarks (and disregarding the special cases + Galarians since SWSH doesn’t give hints on the timeline yet), this is actually their correct age order:
Kanto/Hoenn/Unova1: 21-22-20 (respectively)
Unova2/Kalos: 18-19
Johto/Sinnoh: 17-18
Alola: 11
I had a need to clarify all the age stuff going on 'cause it's been pretty integral with some of their interactions, especially with ships with time gap drama (I don't wanna accidentally make their ages sound weird out of context!), so I hope this cleared up anything problematic!
Their friend groups also tend to be pretty tied-in with their ages!!! The group uses these groupings to refer to each other:
Kids: The Alolans + Oliver, Alex
Teens: Ellen, Gwen, Ophelia, Roy, Hoenn + Galar
"Grown-ups": the "oldies" (Basil, Ceci, Tim), Unovans, Kalosians
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Last thing to address: yes, our new characters not only include our new Galarians, Arthur and Emi, but also a surprise one from the GB timeline, Tim! I hope to share more about them soon! :D