Suicide clusters aren't unheard of, especially among the young, unfortunately. Cornell University in the U.S. has been struggling with recent suicides, for instance.
http://www.suicideinfo.ca/csp/assets/alert36.pdf
http://www.usatoday.com/news/educati...es-16_ST_N.htm
Cause and effect are hard to nail down. I'm guessing that brain development, not completed till the 20s, plays into it. The part of the brain that determines judgment and such isn't fully developed till then.
http://www.actforyouth.net/documents...olbraindev.pdf