Quoted By:
Kanto/Hoenn > 3 years > Johto/Sinnoh > ~3 years > Unova > 2 years > Unova2/Kalos > 2 years > Alola
Therefore, ~10 have passed between Red starting his journey and Elio/Selene starting their journey. If we assume Red, Ethan & Lyra, and Lucas & Dawn are 11 at their starts, Brendan & May are 12, Hilbert & Hilda are 14, and Calem & Serena are ~16.
Thus, following this, as of the time Elio/Selene start their journey, the other MCs are:
Red: 21
Ethan & Lyra: 18
Brendan & May: 22
Lucas & Dawn: 18
Hilbert & Hilda: 18
Calem & Serena: ~18
Therefore, as of Sun and Moon, every MC is an adult, except for Elio/Selene.
Any questions?
