I think you'll find the younger the guy, the more impressed he is with that kind of thing. Most young guys are still enamored by the idea of sex and the female anatomy in general - not having much experience, they're new and exciting. I think with the abundance of internet porn even younger men are still not impressed by shoddy Facebook cleavage when they can spend 0.5 seconds on Google and find fully exposed prize-winning rack. Older men tend to view girls who make a point to post breasty pictures on Facebook as rather one dimensional. If all you're selling is tits, who cares? Been there, done that.