Nova would be fine in agility, they have different sized jumps for different sized dogs. My friend does agility with her two yorkies and my other friend does it with her Pom. At my aunts I do agility with her little Chihuahua, who is 13 years old . As you are probubly coming to see, all sizes and ages of dogs can do agility.
I think you can find some useful information at these links if you'd like to take a look:

http://www,agilityfun.com
http://www.ccdtc.org/

Hope I could help a bit and good luck with Nova and agility