A World War II veteran was asleep in bed when intruders broke into his rural Victorian home, stabbed him in the back 13 times and left him to die slowly on the eve of his 90th birthday.

Jonathon Jeffrey Cooper has admitted fatally stabbing Kenneth Handford at his Springbank home on September 14, 2015.

The 29-year-old was on Friday sentenced to a minimum of 13 years, with a maximum of 16 years, after earlier pleading guilty to the murder of Mr Handford, and for theft and aggravated burglary.

Cooper admits he repeatedly stabbed Mr Handford in the back before leaving his victim tied up on the floor, the Victorian Supreme Court heard.

Justice Jane Dixon said she would have sentenced Cooper to a minimum of 25 years in jail had he not pleaded guilty and offered to testify against an accomplice.