If Eckman violates his probation, he could be sentenced to four years in prison.
Eckman was charged with five felonies and a misdemeanor. He allegedly held a knife at his grandfather's neck and threatened to kill him. Eckman was arrested in June.
Lawyers agreed to drop all charges by one felony account.
Sentencing is scheduled for Dec. 22.
The Associated Press contributed to this report.