Thanks, that's the way we played it "upping maximum rage" but afterward I thought it was weird to be the only stats that didn't have its effect right away.
Like when you pillage a axe, you get one extra VP right away if there was a fight.
It's because the 3 stats are used at different phases:
Rage: used at beginning of the age to determine the amount of rage you can use during that age;
Hammers: used after a successful battle to determine the amount of glory you get;
Horns: used to determine how many units you can have on the board.
Rage is only used between ages while the others are used in the action phase of an age.