Last time I looked, there wasn't any state law that specified an age. Each county/city is going to differ. I know that Salt Lake City itself, has an ordinance stating that they have to be at least 8 weeks old, but that isn't a county ordinance, just the city itself and maybe any annexes that are governed by the city's laws. You would just need to explore the laws of whatever city/county you are in, to know what their laws are regarding this. I personally feel it is best to wait til they are 8 weeks old, just because it seems to be best for their health. I have gotten baby bunnies in the past, at times they have been younger than 8 weeks old, and it seemed the younger they were, the more health problems they had or developed over the years.