I looooveee agility.
I've only taken one class but hope to take more. I practice a bit here and there at home with some cheap equipment.
To do "real" agility -- it's really best to wait until one year of age to ensure joints and growth plates are in place. Actually most agility courses require them to be one year of age. But you can do little things at home like tunnels and putting really low jumps, etc.
Good luck, it's really a blast and a great bonding experience.
Alaskayorkie also does a lot of agility with his pup, Eddie.