I think some people find it somewhat condescending
when they first hear me use the term, but I've taken to calling people kids all the time. I'm not sure exactly when I got on that kick, but as best I can tell, it came about because it's a good gender-neutral
term for "guy."
My almost exclusive use is "Yeah, ___'s a good kid. I'm a big fan." I'm pretty sure that one can't be taken as anything but praise.
It's a term of endearment, really. Unfortunately it seems it connotes immature for some people; what I really mean is more like child-like rather than childish. I sometimes get a look of surprise over a shoulder when I say "G'night, kid," but my smile usually undoes any damage.
So far, anyway.