Well it's not really surprising, is it? I was just out of high school when my 67 was born, my first muscle cars were as a very young sailer, a 69 383 RR and then the V code 70 RR
So these are what I grew up with. While I have "some interest" in antiques like the old 20's and 30's cars, they are not exactly my passion.
So for me, about 55 and newer is my interest
This I bet holds true for the "present day" crowd. Anybody that could afford "muscle" probably started out with something about 10 years old or newer. That is what they will identify with when they get to be "our" ages.