All of the serial number TC records for these guns were burned up in a plant fire so the age can't be nailed down very accurately, I saw one posting where people still had their original purchase receipt and had put together a time line for some of the serial numbers.
The earlier guns didn't have "black powder only" stamped on the barrel, these are called "pre warning guns". I think the warning was added in the mid 80s but I am not sure.
A few pictures of your rifle would help to determine its value, the condition of the inside of the barrel is the biggie, many of these guns were not cleaned properly and have bad bores.