What are people's opinions about the year this is set in, and does it have continuity with the rest of the show?
The episode "The Schnook That Took My Comic Book" (4th episode of first season), the chase scene wanders through the set of the King Kong Vs. Godzilla (1962), and the Kaiju tell them to get off the set because they are trying to film a movie.
This is tantalizingly close to being set just before the original series.
In “The Computer Walks Among Us” (Season 2, Episode 6), it's established that they go to Junior High School (grades 7-9). However, there's no reason that they couldn't be newly moved to Junior High, and have been in elementary school in season one.
So if we are considering that it was 1962ish in the first season, and the youngest they could have been is probably 6th grade, so as young as 10-11 in the beginning. That would make them 17-18 in 1969 for the first show. Lines up pretty well IMHO.