I was just wondering how old I have to be to volunteer

Barb is correct.

From their website...Volunteers must be 18 years of age or older; however, children ages 13 and older may work with the animals if accompanied by a parent or legal guardian at all times. Any student under the age of 18 wanting to complete community service hours for their senior project must have an adult present at orientation and during all volunteer hours.

I believe 18

Please call them during business hours and ask