That's only borderline under half + 7 (23/2 = 11.5 + 7 = 18.5), so it depends on how far into the year the 18 year old is. However it really doesn't matter for her since she's covered by the cougar clause.
Becoming a cougar at age 23 seems pretty weird to me though (not that the 18-year-old version of me wouldn't have jumped at the chance to go out with a 23-year-old chick of course).
A couple years ago I remember a girl on another forum was who like 27/28 saying she had developed a "cougar crush" on Michael Cera after watching Juno.