Being a runaway is a status offense and not a crime. You may well return at age 18 without a GED or high school diploma (and be generally unemployable in any decent paying job), but, you won't face jail time solely for being a runaway. However, people who assist you to run away or avoid your parents or legal guardians can face charged even if you stay hidden until you are an adult. Those crimes will not go away simply because you get older.

Note that there is no place in the US where being a runaway is "legal." What will happen to you if found may vary a bit by state, but if you have been reported as a runaway from AZ, you will likely be detained in any state where you are contacted until arrangements can be made to get you home.