I’m 18 and I want to file my taxes but it won’t let me because it said someone already claimed me what do I do

[Carl]

If your parent's filed a tax return and claimed you as a dependent because they qualify to do so, then when you file your tax return you can not take the self-exemption.

So if this is your case, work through your personal information under the Personal Info tab. One of those screens will have a checkbox on it for "I can be claimed on someone else's return". You have to select that checkbox. Then you can e-file your return successfully.