Juan Rivas was sentenced to life and an additional 13 years and six months in prison earlier this week.
The sentences -- which come after Rivas was convicted on 4 separate counts connected to the stabbing in December 2012 -- will be served back-to-back.
Rivas, 17, stabbed Clara Alvarez to death at her home in the 100 block of East Temple Avenue in late July 2011.
Police found Alvarez's decomposing body during a welfare check days after the incident.
Rivas reportedly robbed Alvarez, 83, after stabbing her.
Police say that Rivas later took off in Alvarez's Ford Taurus.
Rivas also allegedly boasted about the crime before and after it happened.
Police later arrested Rivas while he was driving in the stolen Taurus.