There are stamps on the molded pieces that indicate the date that the piece was molded. If you look at the plastic frame, under the barrel (field strip it first), you will see a recycling emblem and a clock with a two digit number in it. The digit indicates the year it was made and the hand on the clock indicates the month it was produced.
There is a similar time stamp on the trigger assembly. Course this only indicates when the piece was molded, not when the whole thing was put together.