That's a good point that freshmen typically don't have as many kids competing at the upper weights. I'm not taking anything away from the freshmen either, I think it just illustrates how difficult it is to compete with kids that may be 3 years older and more physically mature.
I went to the IHSAA website, according to their records there have only been a handful of freshman state champions, and indeed almost every one of them is at the lightest weight class. Keep in mind, though, that their records only consistently started tracking what grade the competitors were in after the 1981 season.
[table] 103 Al Lummio, East Chicago Washington 1942
120 Ray Webb, Bloomington University 1959
98 Lance Ellis, Indianapolis Cathedral 1986
100 Greg Schaefer, Evansville Mater Dei1995
103 John Sheets, Bellmont2000
119 Alex Tsirtsis, Griffith2001
130 Blake Maurer, Evansville Mater Dei2001
112 Angel Escobedo, Griffith2002
103 Eric Galka, Hobart2005
103 Josh Harper, Mishawaka2006
103 Ethan Raley, Indian Creek2008
[/table]