Both.
To your first question, different countires have different ages of consent. In mine, Scotland (and the rest of the UK), it's 16.
Can have sex legally, move out of home, join the armed forces (can apply a year before turning 16) have medical consultation/procedures without parental/guardian input and consent. So no, 18 doesn't count as underage for me.
In the US, it's also 16 for most states and many countries in Europe either have 14-16 or no age of consent as a legal standard.
Regarding your second question, I despise the misuse of terminology regardless of context and especially when it's due to an over-emotional response to something.
Whenever someone tries the "semantics" excuse to dismiss a correction, they're just showing themself to be at best disingenuous and at worst lying scum that will stoop to any level to appear right.
The difference between peadophillia and hebephillia, is that the former is the single most disgusting perversion that there is, second to none. Mislabelling other things as being it is an injustice to both the victims and people who's lives have been ruined (or worse) by misconceptions of reasons for being on a sex offender register.
Finally, to preempt an obvious assertion some asshat will make, no I don't find either age range to be attractive in the slightest. Young or older, I like women that look like they've finished growing up physically. If they look underage, I will actively go out of my way to avoid them.
