>>50038679The plot of Pokémon Ruby and Sapphire and Pokémon Red and Green are contemporaneous. They are then followed by the equally contemporaneous plot of Pokémon Gold, Silver, and Crystal and Pokémon Diamond, Pearl, and Platinum, which are set three years later. Pokémon Black and White are set an unspecified amount of time after those games. Pokémon Black 2 and White 2 are set two years after those games, and are contemporaneous with Pokémon X and Y. Pokémon Sun and Moon and Pokémon Ultra Sun and Ultra Moon take place two years after the events of Pokémon Black 2 and White 2 and at least 10 years after the events of Pokémon Emerald. Pokémon Sword and Shield are known to take place after the events of Pokémon Sun, Moon, Ultra Sun and Ultra Moon because the Pokémon Sword and Shield Pokédex states that research notes of Type: Null were stolen leading to creating more of these Pokémon, in contrast to the three that existed in the previous games.
Therefore, a minimum of 10 years and a maximum of 20 years elapse between RGB and SMUSUM. So Red is between 21 and 31 years old in SMUSUM.
RGBY/RSE/LGPE > 3 years > GSC/DPPT > at least 3 years > BW > 2 years > B2W2/XY > 2 years > SMUSUM > ? years > SWSH