To get stone walls you'll need to use the effect "Set Tech Status", select the player, the tech "Bastion" and select "Active". If you are using the effect "Set Player Age" but the buildings aren't updating, then you'll need to use "Set Tech Status" For example if you want buildings to have the Fortress Age look, then first use the effect "Set Player Age" and put in 2 (for Fortress), then use the effect "Set Tech Status", and use the tech "Fortressize".