Why did the New Class look so much Younger then the Original Class?

Did you ever notice this? The kids on the New Class seemed to look so much younger then the Original class did when they were the same age. I never really understood that. But then I checked the ages on IMDB.com, and sure enough for the New Class they actually casted actors that were nearly the exact age they should be for the characters they were playing. For the New Class which started in 1993, they cast actors that were born in 1979 or 1980 and were only 13 or 14 years old and perfect for just starting out high school, or at the oldest they cast a 16 year old.

In the Original class the characters should have been born in 1975 to be 14 in 1989 and graduate in 1993. But the actors for the Original class tended to be 1-3 years older and born around 1972 or 1973 and were actually 16 or 17 in 1989 instead of the 14 year old characters they were playing. With the exception of Dustion Diamond ofcourse who was 2 years younger then who he was playing. I don't know why it happened that way, but it was something interesting that I noticed. It made the New Class look so much younger then the Originals because they got the ages so dead on for them.