Lots of people suspect this, but here's some hard data to back it up. In 1993, the General Social Survey asked people whether they like various types of music. There are three that are somewhat similar but that came out decades apart: big band, oldies, and contemporary rock.
To look for a cohort effect, I pooled people into three-year age groups, from 18 - 20 to 72 - 74, to get decent sample sizes. Then I took the year that a group turned 15, as a guess of when your mind is most impressionable to popular culture. Here are graphs showing what percent of an age group "likes very much" the three music styles, according to when they turned 15. Click to see full-size:
People who were 15 in the late '30s like big band music the most, while those who turned 15 around 1960 like oldies the most, and those who turned 15 in 1989 like contemporary rock the most. "Contemporary rock" in 1993 likely meant alternative rock. In all cases, the year when the music style peaked is the year when its greatest fans were 15. This isn't so clear in the contemporary rock graph since alternative rock peaked around 1994, so that those who were 15 then were not covered by the survey. You can tell, though, that it's still going up in popularity after 1990.
These cohort effects are not merely due to young people trying to distinguish themselves from old people -- "ew, that's like my dad's music" -- but also about older people trying to distinguish themselves from younger people -- "these kids these days don't know what good music is!" Middle-aged people hate both their parents' music and their kids' music. So, the simplest explanation has nothing to do with family dynamics or anything like that -- only that generations try to distinguish themselves from other generations.
People my age got lucky and experienced two waves of good popular rock music during their formative years -- I was 14 in 1994 and 24 in 2004. I hate on a lot of the mopier, brooding stuff from the alternative rock period, but to be fair, there was some cool stuff too, especially Dookie by Green Day. I can still play that all the way through several times, moving around to it non-stop. Its stripped-down sound and short songs make it more like the Ramones era of punk rock, and not at all like the overwrought stuff that was popular on MTV's 120 Minutes.
The graphs show that some people from the following cohort like music from before their time, probably because they don't care for most of what's being played when they're 15. Aside from Green Day and maybe a few other current bands, I spent most of my time around that age digging into the mid-late '80s "underground / college radio" stuff: Dead Milkmen, Camper Van Beethoven, They Might Be Giants, Big Black, Mojo Nixon, etc.
I tried going back further to experimental '70s music -- The Residents, Captain Beefheart, Talking Heads, Frank Zappa -- but in hindsight, it was mostly a pose that I struck, and I don't like it nearly as much now as I thought I did then. Except for Frank Zappa's Waka/Jawaka and Grand Wazoo. Snakefinger's music has also left a more lasting impression than The Residents'. The coolest thing I remember about this music is buying it on vinyl, when CDs had become standard. (Joe's Record Paradise in Maryland and Orpheus Records in DC -- are they still surviving?)
Popular rock music has sucked for the past two years -- I have more graphs that show that, just wait (in fact, for several types of music). Probably the last good rock album was My Chemical Romance's The Black Parade in late 2006. By the time another new wave surges, I'll be about 33 or 34, so enjoying it won't be a problem. The real test will be the one after that, when I'll be in my mid-40s. If history is any guide, styles will have come full circle many times by then, and it won't sound so queer to my fuddy-duddy ears.
GSS variables used: BIGBAND, OLDIES, CONROCK, AGE.