Related Rule
Colombia
Practice Relating to Rule 137. Participation of Child Soldiers in Hostilities
Colombia’s Basic Military Manual (1995) provides, with respect to non-international armed conflicts in particular, that it is prohibited to “allow direct participation in hostilities of children under the age of 15”. 
Colombia, Derecho Internacional Humanitario – Manual Básico para las Personerías y las Fuerzas Armadas de Colombia, Ministerio de Defensa Nacional, 1995, p. 75.
Colombia’s Law on Judicial Cooperation (1997) states that children under 18 may not be sent to participate in actual military activities. 
Colombia, Law on Judicial Cooperation, 1997, Articles 13–14.
Colombia’s Penal Code (2000) imposes a criminal sanction on “anyone, who, in period of armed conflict, … forces [minors under 18 years of age] to participate directly or indirectly in the hostilities or armed operations”. 
Colombia, Penal Code, 2000, Article 162.
In 2007, in the Constitutional Case No. C-291/07, the Plenary Chamber of Colombia’s Constitutional Court stated:
Taking into account … the development of customary international humanitarian law applicable in internal armed conflicts, the Constitutional Court notes that the fundamental guarantees stemming from the principle of humanity, some of which have attained ius cogens status, … [include] the prohibition against allowing children to take direct part in hostilities. 
Colombia, Constitutional Court, Constitutional Case No. C-291/07, Judgment of 25 April 2007, p. 112.
[footnote in original omitted]
Upon signature of the 1989 Convention on the Rights of the Child, Colombia stated: “It would have been preferable to fix [the age for taking part in armed conflicts] at 18 years in accordance with the principles and norms prevailing in various regions and countries, including Colombia.” 
Colombia, Declaration made upon signature of the Convention on the Rights of the Child, 26 January 1990, reprinted in UN Doc. CRC/C/2/Rev.4, 28 July 1995, p. 15.