Mauer will not be a rookie in 2005. According to the rules, "a player is considered a rookie unless, during a previous season, he had exceeded 130 at-bats or 50 innings pitched in the Major Leagues; or accumulated more than 45 days on the active roster of a Major League club or clubs during the period of the 25-man limit (excluding time in military service and time on the disabled list).
According to my calculations, Mauer spent 46 days on the active roster (April 6-7, June 3-July 18). So he missed the rookie cut-off by exactly one day.
Hmmm thats interesting Mauer can't be rookie of the year by 1
day.... ( Link )http://mlb.mlb.com/NASApp/mlb/min/news/min_news.jsp?ymd=20041106&content_id=911116&vkey=news_min&fext=.jsp