I committed a crime when 17, if i go to trial at 18???

me and my friends committed a crime, well actually destroying school property which came to $2.000 damage (fire) and we were held in a cell for one night. the school principle will drop charges and talk to the police officer in charge(?) in order to keep our records clean. we already helped restoring the school when the damage was originally $8.000. In 5 months i turn 18 and court trial could be in 6 to 9 months from now. Will i go to jail as an adult or be spared as a juvenile? what depends on even going to the court? please help me i need to know what to expect

The GOOD thing is that the school will drop charges. That will help. A lot. It's between the state and you now to iron this out because the school and you have settled things. You may need to work out the last $2000. If your lawyer can get the state to drop the criminal charge, you're OK.
Some rather young juveniles get tried as adults if they commit serious crimes, such as murder. You should talk to the public defendant. The problem here is that you caused damage that cost several thousand dollars, and it may leave a blemish on your record. Another problem is that you were indeed close to 18 when you committed the crime, and you are indeed 18 now. It's going to be hard to be tried as a minor.
You should talk to a lawyer. This is not legal advice, and I am not an attorney, and I am not qualified nor allowed to give legal advice.

Every state is different, but if the charges are going to be dropped like you said, I would suspect you will have a fine and court costs, as it sounds like restitution has been taken care of from your helping make repairs. You might have to go to a class, or do some community service. You still committed a crime, and will be punished, but I don't see jail in your future, especially if this is your first time offense. Either way the age at the time of the crime is the age that they will look at, however, at this point, that is not a real issue.

Usually a person is charged and taken to trial as appropriate according to the age they were at the time of the crime, NOT the age they are when the trial finally comes about. However, that said, in many states, at the age of 17, you would be tried as an adult anyway. You'll be very lucky (and blessed) if the principal will drop the charges, if that's even in his authority to do. Plus the work to help restore the school will be seen in your favor. I hope this will steer you to a better path in life.

in such a serious matter, you should have an attorney to advise you - you don't want any surprises at the last minute!

but you will be charged as a juvenile for sure!

You will be considered the age that you were when you committed the crime and treated accordingly.

btw...people who vandalize really SUCK! STOP IT!