Is it this one?
www.smyrnaschoolofballet.com
This person was (back in January) looking for intensive in ballet, tap and/or jazz for adults. I haven't seen anything like that except for adult summer intensives aka adult dance camps.
At age 18 though, it shouldn't be unheard of to get involved with some school's program that's already set up for those younger dancers. I'm sure there's something to get into without worrying about your age. 18 is only 3 years older than most of who I've seen in those programs.
I recently had a show partner who is 22 and in those kinds of classes. She is high-intermediate or better... probably even advanced. That's the only way to remain in practice at that level since she is en pointe and all that. There are different reasons for those above age 15 to join those classes. It does happen, so see if that's a possibility.