My partner always kissing his DCs on the lips (ages 16-22, male and female). I find this very uncomfortable - he sees them 50/50, at least 3 times a week so it's not like he doesn't see them often, when they come in he sits there with his lips puckered and they all kiss him on the lips, a couple (there are 4) look uncomfortable.
AIBU to think you don't do this once they are practically or are adults? I hug and kiss my 18yo son (on the cheek) but this lip kissing makes mE uncomfortable, especially as the kids get older.