I'm not sure of your age at the time of the alleged offense and the date of the alleged offense so I can't calculate the applicable time period for the statute of limitations which would apply to the charging of the crime.

What I can tell from the question is that unless the period from the date of the discovery of the offense by the Government to the point of actual charging of the offense is greater than the statute of limitations, a person who committed a crime as a minor, about to become an adult, can be charged when that person reaches adulthood (majority).

Just reaching the age of eighteen doesn't make the allegation of an offense go away, it just changes the legal status of the accused from accused as a minor to accused as an adult. The statute of limitations is addressed under A.R.S. § 13-107.