Is an 18 yr old high school student considered a "full time student" or does this only apply to college kids? He just turned 18 in November.

High school counts as being a full time student.  But that doesn't matter, in your case, because he is under 19.

There are two types of dependents, "Qualifying Children"(QC) and Other ("Qualifying Relative" in IRS parlance even though they don't have to actually be related). There is no income limit for a QC but there is an age limit, student status, a relationship test and residence test.

A child of a taxpayer can still be a “Qualifying Child” (QC) dependent, regardless of his/her income, if:

1. He is under age 19, or under 24 if a full time student for at least 5 months of the year, or is totally & permanently disabled
2. He did not provide more than 1/2 his own support. Scholarships are excluded from the support calculation
3. He lived with the parent (including temporary absences such as away at school) for more than half the year

Because he is under 19 and lives with you, you can still claim him as a dependent.  TurboTax picks up his age when you enter his birth date.  You are also asked how long he lived with you in 2022 (most parents answer all year).