I could be wrong, this may not apply to this bike, but... check the Schwinn nameplate. At least on mine, there's a four digit code stamped into it.
That code will be the day of production in the year, and then the last digit of the year.
Then, look on the frame, near where the derailer used to be, and look for a five character code. It'll probably start with a letter which indicates where it was produced. You're going to be interested in the last four digits - two digit month, two digit year.