With regards to the latter, 'kids' is often used to refer to a group that is a) younger than the speaker, or b) acting juvenile (sometimes in an affectionate manner: 'Have fun, you crazy kids,' can and has been applied to an older couple getting all fuss-and-bothered about a special night out.)
In a similar manner, a woman of any age might say her husband (also of any age) is going 'out with the boys', or that she is having a 'girls' night out'. This can be used in an insulting manner (as GL said), but if it's referring to a group, it's more acceptable. Also, see the terms 'boyfriend' and 'girlfriend', which are still used regardless of age, when people don't want to say 'significant other' or 'S.O.' A lot of it is tonal and situational, as well. the word 'boy', used in place of a name is insulting, even more if delivered in a clipped, imperious tone, and I'd be willing to call it 'fighting words' if the addressee is of non-Caucasian descent.
As far as the superhero angle goes, sidekicks are more often to keep the 'boy' tag a bit longer, especially if they are part of a 'mentor/student' sort of team (Robin, the Boy Wonder and Aqualad come to mind), but once they hit solo, it's more common to see them lose that (Nightwing).