In the process of tinkering with some fanfic on Daria in college, I decided to assume she graduated Lawndale HS in spring 2001, and went to Boston in fall 2001. It worked out better for dramatic purposes. This implies she turned 19 in fall 2001 (from what others say here about her being a Scorpio or November baby), and was born in 1982. Quinn would then have been born in the spring of 1984 (and one can only imagine what Daria has made of THAT birthyear-timing in the past!).
Of course, then, Helen & Jake, being in their (I assume) upper 40s, were born in about the mid-1950s and remember Howdy-Doody. Oh, boy.