What is the test for determining whether a punishment is grossly disproportionate to a defendant's individual culpability?

In addition to the consideration of the nature of the offense involved, we must also consider "the nature of the offender" to determine if the punishment in question also fails to fit the criminal. ( People v. Dillon, supra, 34 Cal.3d at p. 479, 194 Cal.Rptr. 390, 668 P.2d 697.) In this regard, courts determine whether the punishment is grossly disproportionate to the defendant's individual culpability as shown by such factors as his age, prior criminality, personal characteristics, and state of mind.