Wait a year.
That goes for any tattoo you might want in the future. Considering you've got almost a year to wait anyway, I would say wait until next year still, and use the extra few months to really think on it. Over that waiting period, you can think about if you're really excited about the idea then as you were when you first started wanting it. And by January next year, which isn't that long of a wait after you turn eighteen, ask yourself if it's something you really want or something you're glad you didn't actually get. A year isn't that long, and if the tattoos would still hold some meaning to you by then, then there you go. Some people wait even two years or longer so they can be sure they wouldn't have regretted getting the tattoo they thought they wanted. It's up to you, though, and whether you think you're ready for that kind of commitment or not.