The presumption is that seminary candidates aren’t or might not be emotionally mature. One question: are seminaries really the ideal place for developing such maturity? Granted, all of us have some growing up to do. A healthy and integrated person is always finding room for improvement, if not a deeper sense of sin and contrition. Sounds like something more suitable for a people in their thirties rather than teens.
317. We recognize the effort of those who are charted with formation in seminaries. Their witness and preparation are decisive for accompanying seminarians toward an emotional maturity that will make them suitable for embracing priestly celibacy and able to live in communion with their brothers in the priestly vocation; in this sense, the courses established for those in charge of formation are an effective means of aiding their mission. (In this regard the synod fathers exhort bishops to “assign the most suitable priests to this work, after preparing them with specific training for this delicate mission” EAm 40; Congregation for Catholic Education, Ratio fundamentalis institutionis sacerdotalis, 31-36; ID., Guidelines on the preparation of those in charge of formation in seminaries, n. 65-71; OT 5.)
Comments?
For deeper examination, an English translation of the 2007 document from the Aparecida Conference.
Catholic Sensibility 
There was a book I read a few years back called something like Sex, Codes and the Catholic Church, in which a reference was made to Catholic based studies done by their own internal psychiatrists. These studies determined that the overwhelmingly majority of seminarians *and* subsequently priests, had a disproportionately high level of sexual immaturity and mental disorders.
Of course the book, written by four bravely outspoken priests (some still active within the Catholic institution) covered other interesting data as well, and successfully, in my opinion, exploded the myth of the *celibate* priest. They advanced the argument that the suppression of natural relations with and trust in women, and the seminarian lifestyle in general, groomed particularly vulnerable men into active sex lives mostly with each other, and their compromisation allowed for the predatory behavior of authoritative brute homosexual clerics above them.
I would have a hard time arguing against some of these points. It has always struck me that seminaries attempt to reproduce an environment more similar to religious life. Then newly ordained priests are placed in what most monastics insist is decades in the making and only for a select few: the life of a hermit. Our seminaries, bishops, and traditional-leaning Church have done many priests, probably most of them, a deep, deep disservice.