I'm 41 and it's been that way for at least as long as I've been alive. All the stores carry the same clothes, all the cars look alike, even shoes, jewelry and belts become similar. It's driven me crazy ever since I became sentient.
But then, even teenagers who dress in an effort to be "different" look the same as each other. I noticed that in the '80s when I saw a cluster of teens all with variations on spiked, dyed-black hair, olive green trenchcoats and combat boots.