Eighteen symbolizes the conflict between materialism and spirituality. It also warns of treachery, deception, lies, and selfishness.
To see the number eighteen in a dream foretells a calamity, but you will escape unharmed.
Dreaming about age 18 can represent newness, beginning a phase, making a fresh start; or responsibility, freedom, self-sufficiency, validation. It could also mean there are things you need to learn through experience (learn the hard way), as is often true at age 18.