I believe the tutorial for this is part of the "building your first Age" tutorial.
Essentially, make the mesh you want to be your collider. Set it to triangle mesh (or other types of collision) and add a string property, set Name to "type", and set the last field to collider.
This object should have no material or UVtex or color or anything set to it.
In the Object panel, under Draw, Drawtype. Set it to Wire.
And you're done. It's great to use when you have a large and complex object but only part of the object needs to have collision. Separate that part of the mesh and set this up as your collider. Can help you save Age file size