As used in this Section, "ransom" includes money, benefit, or other valuable thing or concession.
A person who has attained the age of 18 years at the time of the commission of the offense and who is convicted of a second or subsequent offense of aggravated kidnaping shall be sentenced to a term of natural life imprisonment; except that a sentence of natural life imprisonment shall not be imposed under this Section unless the second or subsequent offense was committed after conviction on the first offense. An offender under the age of 18 years at the time of the commission of the second or subsequent offense shall be sentenced under Section 5-4.5-105 of the Unified Code of Corrections.
720 ILCS 5/10-2