Clunker from Perth

I just got home from spending a couple of weeks in Perth.  On the way back I intentionally booked a flight on the old 747-300 operated by Qantas (Perth to Melbourne).   The aircraft I was on is 21 years old.   I actually thought it was older.  The Economy/Business configuration of the 747-300 allows Qantas to squeeze in 450 people.   That might explain the long wait for my bags at the carousel in Melbourne.
I enjoyed my ride on the old jumbo.   Qantas still has 4 of them in operation on the east to west coast routes.   I was surprised to see them fitted with video on demand screen at every seat.  Not even United long haul jumbos have this!   But I’m mostly interested in the real age of the Boeing 747s.  Does anyone know what the first model was and when it was built?    I have heard that the earlier models are not allowed to seat passengers upstairs because there are no exit doors up there.   I think some of the Asian airlines still have them.    I was also curious because my 747-300 still had ashtrays.  I guess we’ll be seeing more of the 747 fleet flying domestiv routes when Qantas starts receiving the new A380s later this year.