Son Turns 18 Soon So Can I Still Collect Child Support

I reside in Copley and my ex who lives in Lake County and is the custodial parent has discussed the possibility of our son coming to live with me upon graduation from high school or before. Our son will turn 18 on Feb 27. I was wondering if I get him before graduation can I file for child support even though he is now 18. He may not graduate because of grades and will have to attend summer school thus can I get support if he has turned 18 but not graduated. The court order currently does not discuss child support as I have not ever paid any child support in the nine years my son has lived with his father. Once 18 can he just come live with me without a court order changing custody? I just want to get money from my ex husband b/c he feels like he should get the dependency deduction on his taxes just because he provides all the support and I figure that if i can convince my son to come live with me I can get more money from him without ever having to pay him a dime.I love how the system favors women b/c when I had him he had to pay me support and when custody changed in 2001 I was able to threaten to take him back to court if he filed for support. I actually did file for a change of custody once pro se and my ex husband had to hire a lawyer and lost over 3000 on the retainer b/c I never even showed up again but his lawyer did. I told him if he mentioned child support again I would keep filing these cases and even if he did file for support he would pay more in legal fees and all the other associated fees with these cases such as court psychological and gal.