@Momosuke Well in Europe in certain countries you'll have parents kissing their very young children on the lips (a simple peck on the lips, nothing more). I was raised like that until I was around 3 yrs old, as which point I received kisses on the cheeks or forehead instead. It's considered okay until a certain age, after which it becomes weird because the child is too old.
Also, I frequently greet friends of either gender with a kiss on the cheek but I know that in other countries they greet people differently and consider a cheek kiss to be too much.
Greetings can be different depending on countries.