A couple of Governors had their hands on the age limit issue after Measure 11 required definite sentences.  

From OYA Website:
The modern era of juvenile justice in Oregon began in 1995 with the passage of Senate Bill 1. This legislation:
•Implemented Ballot Measure 11, which requires fixed sentences for youth and adults committing violent crimes; 
•Prescribed a tiered system of sanctions for juvenile offenders; and 
•Established the Oregon Youth Authority (OYA).
Senate Bill 1 was the culmination of the work of the Governor´s Task Force on Juvenile Crime, which was appointed in 1993 by then Governor Barbara Roberts and chaired by then Attorney General Ted Kulongoski. The focus of the Task Force was to expand the capacity of Oregon’s juvenile institutions to meet growing needs and to ensure that juvenile offenders were appropriately held accountable throughout the juvenile justice system.