In my own personal collection of music in mixes and playlists I have used a different breakdown of musical eras. My groups are still about ten years but my time span is based more on style and culture rather than the calendar.
My first decade of rock 'n' roll begins about 1956 and goes to 1965. I call it the First Decade and includes a variety of music from the early pioneers of rock 'n' roll, Elvis, rockabilly, doo wop and early Motown, the Beach Boys and surf music, Buddy Holly, Chuck Berry, the girl groups, the Four Seasons, early British Invasion, those first few Beatles albums, the early Stones and the blues men such as Howlin' Wolf and Muddy Waters.
The Second Decade starts about 1966 or thereabouts because Rubber Soul was 1965 and that album really shows the difference in the decades. It was the beginning or what came to be known as Classic Rock. It was also a decade of soul music and the beginnings of funk and reggae. Classic country too.
The Third Decade starts in 1977 but that again is arbitrary because you could see the changes coming a little earlier in bands like the Ramones and Big Star. Of course the really big thing about this decade is Punk, New Wave and Disco. Why limit this era to 80's music when artists like the Clash, Talking Heads and Elvis Costello began in the 70's with essentially the same sound. There is also the early Rap and Hip-Hop starting at this time.
The Fourth Decade runs from the mid 80's to the mid 90's and includes what is sometimes called Modern Rock, Post Punk, Grunge, Rap and the assorted smaller genres that music seems to have been obsessively broken down into.
The Fifth Decade hasn't really jelled into something really unique or discernible yet. It is still too early to tell. All those Alternative genres and endless sub genres abound. Post-Rock I guess and all the various Alt-this or that. So here we're talking about the mid 90's to the mid 00's.
Now we are already half way into the Sixth Decade.
Here is an example of using my decades concept for a mix.
This might be called an 80's mix but it really is a Third Decade mix. Message of Love.
Here Comes Your Man is a Fourth Decade mix. It sounds like a certain time but not limited to a specific decade. The songs range from 1987 to 1996 which is the fourth decade of rock music.
So this is all just meaningless ramblings while I sit at my laptop listening to some great music.