Amends the Unified Code of Corrections. In provisions that specify offenses for which a period of probation, a term of periodic imprisonment, or conditional discharge shall not be imposed, provides exceptions for certain offenses in cases where the offender is under the age of 26 at the time of the offense. Provides that, at a sentencing hearing, the court shall consider the developmental appropriateness of the sentence and apply great weight to factors of youthfulness such as the diminished culpability of youth and young adults as compared to adults and capacity for growth and maturity.