Is it normal that i don't consider 18 to be an "adult"?
People say how 18 means you're an adult but I believe otherwise:
1) The human mind doesn't stop developing until mid 20s
2) People this age are more commonly still immature than completely as a true adult would be
3) This one's obvious but it has "Teen" in it.
4) People this age still tend to be dependent on their folks
For me, one's not an adult until the age of 20. But that's just me.