Understanding Stages/Restrictions

So before going deeper let's figure out how a Stage is different from a Restriction.

A Stage is a way for the mod to know which restrictions should be applied to the player. Example: You've created a stage named "age_1" and there's a player which doesn't have it, the mod will seek all the restrictions and see which one of them is bound to the stage named "age_1", after that the mod will go through all the items/blocks/tags/mods etc. that the restriction has and do what that restriction is configured to do.

A Restriction is the way the mod hides items from JEI, drops items from the player's inventory, doesn't allow the player to interact with blocks/items, checks if the player has an item which he shouldn't be allowed to use in a certain container (useful for restricting recipes).