Mont. Code Ann. § 39-71-602

No limitation of time as provided in 39-71-601 or in this chapter, known as the Workers' Compensation Act, shall run as against any injured worker who is mentally incompetent and without a guardian or an injured minor under 18 years of age who may be without a parent or guardian. A guardian in either case may be appointed by any court of competent jurisdiction, in which event the period of limitations as provided for in 39-71-601 shall begin to run on the date of appointment of such guardian or when such minor arrives at 18 years of age, whichever date is earlier.