I think of 20+ as adults because some 18 year olds are still really immature, even though they are legally adults.
I think the legal adult age is 18 but than again they say age 21, it's really complicated..It would be something if the legal age of adult became just 21.
I think them as adults!
Technically 18 year olds are considered adult, that being said, I have seen 18 - 20 year olds less mature than my 11 year old niece.