The Kentucky Supreme Court ruled Thursday that the mental age of a death row inmate does not prevent the state from executing him.

An attorney for Thomas Clyde Bowling had argued that the inmate had the mental capacity of an 11-year-old when he killed two people in Lexington in 1990, citing testimony from psychologists.

The state high court in Frankfort noted the U.S. Supreme Court's decision last year barring executions for killers who were not at least 18 years old at the time of the crime, but said the ruling did not specifically prohibit putting to death someone with a mental age below that.

"There is simply no language to support such a conclusion," Justice Martin Johnstone wrote in a 5-0 opinion.

Johnstone wrote that there is some validity to the idea put forth by Bowling's attorneys, but that the federal high court intentionally established chronological age, not mental age, as the deciding factor.

Defense attorneys have 20 days to ask for a rehearing from the high court and they said Thursday they would seek one.

Bowling's attorney, David Barron, said he was heartened that the court said the mental age argument had merit.

"This court recognized this as a valid legal concept that all courts should be concerned about," Barron said.

Vicki Glass, a spokeswoman for Kentucky Attorney General Greg Stumbo, called the ruling "an important step toward carrying out the jury's verdict."

Bowling, 53, also has asked a federal judge to stop his execution on the grounds that he is mentally retarded.

The state supreme court rejected the claim last year, saying they found no conclusive evidence that Bowling was mentally retarded. His IQ has ranged from the mid-60s to mid-70s in different tests.

A U.S. Supreme Court ruling in 2002 bars execution of the mentally retarded as unconstitutionally cruel, but left states to decided how to ensure that mentally retarded people are not executed.

In a case still under review by the Kentucky Supreme Court, Bowling also has challenged the legality of lethal injection.

Bowling originally was scheduled to be executed in November 2004 for shooting Lexington residents Eddie and Tina Earley outside their dry cleaning business. Their 2-year-old son also was shot in the assault but survived.