The Columbus Ledger-Enquirer reported that Ethan C. Welch admitted stabbing his maternal grandmother, 59-year-old Brenda Cook with a steak knife and meat skewer outside their home in 2009.
Welch said nothing during Monday's hearing, except to say "guilty" when Muscogee County Superior Court Chief Judge John Allen asked how he would plead.
Prosecutors charged Welch as an adult, and Allen said he had no alternative but to sentence him to life in prison. Welch will be eligible for parole in 30 years.
Defense attorney Stephen Craft says Welch didn't want his family to have to go through a trial.