I'm pretty much the same...a social butterfly. Though not extrememly outgoing, but I don't shy away from confrontations, either. I, too find myself sometimes over-applying humor to most given situations, resulting in making some take a seeminly second glance...lol, which is perfectly fine with me.
When I encounter those who are non-responsive to "lightening up", then, so be it....I don't think twice about it as it's hard to know what they're like, how they deal with social situations, etc. For all I know, they're struggling inside seeking ways TO relax and interact with more ease. Still, it isn't anything I ponder upon after taking notice to.

I think, too, that it depends on how well you know the person, if the person wants help to come out of their shell, if they can come out of that shell, and if they've asked for that help. Outside of that, I'd think that, yeah, there's little to no chance of someone else showing them the way.

I don't think it's ever too late to strive for improvement/change, so long as there is that inner will TO acquire change, (so I don't think age is really the issue). However, imo, depending upon the individual, obtaining change can be very unlikely especially if they are suffering from any disorders which prevent them from feeling comfy with their own selves? I'm really not sure.

Sure, behavior is something we all Learn from early on and some of those behaviors we do carry into adulthood, again all depends upon the individual, if they suffer from any disorder, or not, and if the behaviors are something that they are happy with, or not. It's really hard to say.

What I've learned when encountering those "reserved" types (who wish to be reserved), is I just allow them to be who they are without giving it a second thought.... What more can you do?

Shangrala