As a 41 year old, when I call someone in their early-mid 20s a kid, there’s no derision intended. Think about how you relate to someone who’s 12 or 16 when you’re 20 or so - they might be quite capable, even fun to hang out with; but their life experiences also give them a clearly different outlook. And, like as not, you feel a little more interest in making sure they’re getting along all right (at least I do!)

As you age, that doesn’t really change - but the “target age” where that comes into play follows you up! So at 26, you feel that way about people just coming into high school; at 30-35, about people getting out of college and starting their careers. My oldest kid is 6; and I feel this way now about most of the parents of my kids’ classmates! Makes for a fun juxtaposition, when they have older kids and know more about what we’re in for than I do :p

It can turn into something condescending, depending on the person; but I think it’s usually more of a statement that “I remember being where you were!”