I'm not 18 and 1/2 yet

Can someone answer this for me real quick.

I'll be 18 by October 31. Though I wont finish my senior year till May 21st .

If I leave before turning 18 1/2 what process would I need to go through before entering the country legally. Is there a good chance in it? How long would it be before I would be back.

Also I have to finish High School before leaving. Can I get an extension before I am penalized for 3 years? If it does not seem so hard to return on a legal status I'm willing to finish my last year early.

you're chances are 0 , k honestly they might let you come back in 15 years. or maybe 35