My bro had one when we were much younger years ago, and living in Ohio.
He was 7 and I was 8, and we didn't know much of anything about fish, so he had the little guy (we bought him when he was about 3 inches) in a 20 gallon.
He lived for about 6 months before we had a pretty bad ice storm and lost power for a couple days.
We think he froze since like I said, we didn't know much, and had it in front of his bedroom window : (
As for having them before they were made illegal, I'm not sure. I know when we moved from Ohio to Cali, we couldn't bring our ferret, because the grandfather clause required you to have it while living in that state before it was made illegal. We had him in another state were he wasn't illlegal, so it didn't apply to us.
However, I think they're a bit stricter on snake heads, than ferrets or gerbils.