In fact, in the U.S., it's legal (but never done) to specify ranges on educational matriculation. A company could "back-door age discriminate" by setting a policy of "must be no more than 5 years out of school". When one attended school is a legal question, although age is not.
The major effect of it is to discourage people who take HR requirements seriously, who haven't figured out that "5 years experience" means "intermediate competence" and can be achieved in 1 really good year, or not achieved in an endless number of mediocre years.
I've been analyzing the MacLeod hierarchy (Losers, Clueless, Sociopaths) over the past month: http://michaelochurch.wordpress.com/2013/02/19/gervais-princ...
MacLeod Sociopaths aren't actually bad people. I'm a MacLeod Sociopath and don't think I'm a real sociopath. They're a mix of chaotic-good rebellious rulebreakers, chaotic-neutral people who enjoy problem solving for its own thrill (and will be very helpful and altruistic if given appropriate challenges challenges, and destructive if let to rot), lawful- and neutral-evil liars, cheats, and psychopaths. (Chaotic evil is severely socially dysfunctional and not much of a presence.) MacLeod Sociopaths break rules and often live on the margins, and will either rise fast or get fired. There are "good Sociopaths", but even for the good kind, most companies would prefer to hire only a few.
These HR walls favor the MacLeod Sociopaths who have no qualms about applying to a job requiring 5 years of experience when they have 6 very good months. It's not that "rules were meant to be broken" (that's false and insane). It's that rigid rules keep so many people out that the only people breaking through are the ones who disregard rules or find back doors. Of course, there are good rule-breakers out there, but you have to be careful with even them.
The same problem exists around reference checks. For executive hires, larger and risk-averse companies require 10-20 references. At ten references, you're selecting for sociopaths. Only a colossal fuckup can't get 2-3 good references, but most people don't have 10 glowing ones. Ten glowing references is a sure sign that someone not only coached, but quite possibly extorted, a few people. It's not a guarantee that you'll get a bad person, but you will get a rule-breaker if your HR wall is that impenetrable.