Unlike previous Mainstream Pokemon Games, every Pokemon Gym found within this game have certain requirements that must be met before your trainer will be allowed to challenge said Gym. The sixth Pokemon Gym within the Kanto Region is found in Saffron City. This Pokemon Gym is full of trainers that have Pokemon at or above Level 40, and because of this, your trainer will be required to have at least one Pokemon at Level 45 or higher in their Party in order to gain access to the Gym. (Much like the Pewter City Gym and Cerulean City Gym, it isn't required to battle with the Pokemon you used to gain access to the Gym while inside of it.)