How can I tell if my CAG is a boy or a girl?

There is no definite way to tell the sex of a Grey unless it is either surgically (not advisable) or DNA (advisable) sexed. However, there are a few pointers which can be used, notably the under tail coverts; the shorter red feathers. It seems that the females have a delicate silver edging to these feathers whereas the males have solid red feathers. This must not be confused with the dark grey or black edging that young birds often have on their tails and it might not be seen until after the first molt. Red feathers around the vent are not at all conclusive as these are seen on both males and females. Males are also said to have broader, squarer heads while the female head is rounder, and the males beak tends to be larger. However, because Greys vary in size, this can be difficult to see because it is perfectly possible to have a smaller male and a larger female.

Jane

The first two photos below are of Mitzi's tail, the second two are Tanna's Isoke, showing what to look for and what to disregard.