>>51362642>>51363640>Serena/CalemThis is a fun one. In the post-game, you can access Team Flare lab files on the homeless girl Emma they were experimenting MK Ultra style on. She's stated to be 16, and noted to be younger than Calem/Serena. This means that Game Freak did in fact continue the trend of aging up the protagonists each Gen, with Calem/Serena being 16-17 throughout their journey.
>Elio/SeleneIt seems the trend of aging up the characters ended here, as it's explicitly stated at the start of Sun/Moon that you, like all kids who go on the Island Challenge of Alola, are 11. It's worth noting that you're also said to come from Kanto (a tease for LGPE and nod to the concept of Regional variants, which was exclusively featuring Kanto Pokémon at the time. Your mother even keeps a Kantonian Meowth in her home.
>Gloria/VictorThe trend of non-Japanese regions seemingly having older protagonists appears to continue here. There is technically no confirmed age for these characters, but proportionally they look far, far closer to Gen 5 or Legends Arceus characters, than they do Gen 7 or the older games. This would assumedly put Gloria and Victor at about 14-15.
Gen 9 kinda threw everyone for a loop with its school setting, and appears much closer in design style to Gen 7, so I assume those new characters are back to 11 again. Bit of a shame, I feel like the mid-teens look of the Gen 8/Legends characters were the sweet spot of "childlike wonder" and "coming of age adventurer", which appears to be what Game Freak wants in a Protag design.
But anyways, there. That's to my knowledge, all the info based on in-game knowledge or educated guesses, of the Protagonists ages. If anybody has additional knowledge or info, feel free to add.