There's no reason to assume people will instantly like a band that hasn't been active for 42 years just cause they were popular then. I'm willing to bet the reason their fame carried on for so long after their active years is because of parents raised in the 60s and 70s influencing their kids. Now generations are beginning to shift to the point where peoples' grandparents grew up with the Beatles.
Like you said, age shouldn't matter. People will like what they like, regardless of age. If teenage girls favor what they were raised with, why is it a problem?
That's how it works. You take a liking to the music you was raised on.
I was raised on country.
My sister was raised on I have no loving idea what she listens to.
A dude I know was raised on rap
So on and so forth it depends on how you was raised on the music you listen to. One of these days Rap, Dupstep, and screamo will be the "Golden Oldies"