My experience is they don't want TOO young, because most of the people making the hiring decisions are 45-55, and they don't relate well to the 21-25 yr olds, because the 21-25 yr olds are the first TRUE internet generation (i.e. they had intense, massive internet/computer exposure starting in high school).
My generation (somewhat caught between GenX and GenY) is people who learned internet/computer in college or later, and some of us didn't really become adept ever, or until very recently. We don't really have the innate "figure internet/electronic stuff out" characteristic that most GenY have.
I think history will record this time as an abrupt shift. Much like it must've been strange for the older people to relate to the first generation of Americans who drove a car on their 16th birthday.
Also, sadly, i believe there has been a MASSIVE "dumbing down of America" over past 20 years, but its effects are seen most in the GenY generation. Some of them, who seemingly have great grades, great stats, great resumes, etc. are actually IDIOTS. Its really sad. I think the schools have a new stupid idea that "everybody can be right in their own way" and of course the infamous "grade inflation" which is real.
And also, i HATE that so many people now take massive tutoring and massive PREP-type courses for taking certain grad school **103** exams (like MCAT or LSAT). By doing so, those idiots do much better than historically their IQ has done, thereby flooding the med and law schools with morons.