I was wondering if an 11 year old were to volunteer for their service hours, could they only serve once?

Probably best to ask CAT directly.

You must be 12 years of age or older and must volunteer with an adult and they require a commitment of at least eight hours a month in order to go through the training required to volunteer at cat

I don't think so. They have a training for all the volunteers, and I believe a commitment for more than once. commitment

It would be best to inquire in person