A friend of mine noticed this while watching the show. If you look at the beginning, they show a license plate from the car they are sitting in during the opening credits and the year on the registration sticker is incremented every season and, presumably, represents the year the show is taking place in. The current season is in 1979, so who knows what will happen if they make it another year. I believe they are all seniors in High School in current season (being shown now in 2002). One hopes this does not lead to a reincarnation of the horrible That '80s Show which was blessedly cancelled almost as soon as it began.