The number eighteen is related to the adult life, where the person is entering the new phase of his/hers life.
Dream dictionary: Eighteen dream meanings
…up endless staircases and along the most blood-curdling corridors, has at length cornered me in a gloomy top attic. All seems hopeless, and I am expecting to be caught every second, when, just as the dreadful creature bounds into the room, I leap on to the window-sill and, with a prodigious bound, spring into space. And then, joy of joys, instead of falling, I find I can fly fly far away into the distant, boundless heavens where there is nothing to stop me.I have carefully counted the number of flying-dreams I have had in twelve months, from January 1,1910, to January 1, 1911, and find they amount to eighteen truly, a fair percentage! And what happens after them? Generally a surprise visit, or unexpected journey or letter, or unusually heavy correspondence nothing more serious. But as dreams go, I know of few that are more fascinating….