Is it possible that thought/communication disorders occur at 18 years old stemming from schizophrenia?

Yes, that is the age: Perhaps the most likely age range for appearance of schizophrenia is 17 - 24. Thoughts as well as communication are often areas that are noticed to be different than before. Other symptoms would also be necessary for a firm diagnosis, but it is a possible one. Find a really good psychotherapist with experience in evaluation of psychosis and alternative neurological problems. Good luck.