Nowdays you can't really do this. but there's a way get around the age in the past and be considered as adult.
That is. Just get married. During my middle school days and ( up to 20 years ago or so). There's quite few who would get married after graduation. Even when you are 13, 14, 15 etc you would be legally an adult. Have Id, can take a loan, vote and all the adult thing. You can do it.