WASHINGTON — Joe Sullivan was sent away for life for raping an elderly woman and judged incorrigible though he was only 13 at the time of the attack.

Terrance Graham, implicated in armed robberies when he was 16 and 17, was given a life sentence by a judge who told the teenager he threw his life away.

They didn't kill anyone, but they effectively were sentenced to die in prison.

Life sentences with no chance of parole are rare and harsh for juveniles tried as adults and convicted of crimes less serious than killing. Just over 100 prison inmates in the United States are serving those terms, according to data compiled by opponents of the sentences.

Now the Supreme Court is being asked to say that locking up juveniles and throwing away the key is cruel and unusual — and thus, unconstitutional. Other than in death penalty cases, the justices never before have found that a penalty crossed the cruel-and-unusual line. They will hear arguments Monday.

Graham, now 22, and Sullivan, now 33, are in Florida prisons, which hold more than 70 percent of juvenile defendants locked up for life for nonhomicide crimes. Although their lawyers deny their clients are guilty, the court will consider only whether the sentences are permitted by the Constitution.

The Supreme Court's latest look at how to punish young criminals flows directly from its 4-year-old decision to rule out the death penalty for anyone younger than 18.

In that 2005 case decided by a 5-4 vote, Justice Anthony Kennedy's majority opinion talked about "the lesser culpability of the juvenile offender."

"From a moral standpoint it would be misguided to equate the failings of a minor with those of an adult, for a greater possibility exists that a minor's character deficiencies will be reformed," Kennedy said.

Yet Kennedy also acknowledged the possibility that for the worst crimes and the worst offenders, "the punishment of life imprisonment without the possibility of parole is itself a severe sanction, in particular for a young person."

Both sides point to the same basic facts — the rare imposition of Draconian prison terms on people so young — to make their point.

The state of Florida, backed by 19 other states, argues it should retain flexibility in sentencing so that "particularly heinous acts that stop short of causing death" can be punished vigorously.

Life without parole "is appropriately rare and reserved only for the worst of the worst offenders," crime victims' groups said in court papers.