Why are NPCs defining my character's age?

I don't know if this bugs anybody else, but ... one of the "rules" of roleplaying (and this is a roleplaying game) is that you should never mandate what other characters are thinking or feeling or how they react to something. For example:

Wrong:

"I punch you in the face, and you scream in pain and crumple to the ground."

Right:

Character 1: "I punch you in the face."
Character 2: "I scream in pain and crumple to the ground."

Now, I'll make allowances for game mechanics necessitating letting the game describe how my character physically reacts to things, like if my character gets hit with a knockback and fails to resist it, she falls down, or if she takes enough damage she's "defeated".

But this can and should be avoided in ordinary dialog with NPCs. IMO there is absolutely no justification for an NPC telling me anything about my character beyond what can be physically observed and verified (and if they do know other things about my character, there should be an explanation for how they have this information — "According to the Vanguard files on you..."). Specifically, I find it extremely annoying when Twinshot (and later, Maelstrom) keeps calling my characters "kiddo". Sure, when my characters first meet Twinshot, they are "novice" heroes and she's a more experienced hero. But "novice" =/= "young". Yeah, most of my characters are young. But some of my characters aren't. I have a few human characters who are clearly older than Twinshot. I have some characters who are aliens, whose ages Twinshot cannot possibly guess. I have some Magic-origin characters who are members of "fantasy" races, whose ages Twinshot couldn't know. My petite, fairy/elf-looking brute with the cherub wings could be an immortal who is thousands of years old, and only looks seventeen because she doesn't age normally. And while I don't have any robot characters, I could make one, and that robot would certainly not be a "kiddo" (or an "old man", either, for that matter). Just the simple fact that the character creator has "Older Faces" options should make it obvious that not every character is going to be young, and therefore NPCs making age-specific comments about player characters is inappropriate.

Listen, kiddo, just because someone calls you "kiddo" doesn't mean they're saying anything about your age.

(see what I did there? )

In all seriousness, kiddo != young. It can be used that way, or it can be used the same as any other term like it.

We've been saving Paragon City for eight and a half years. It's time to do it one more time.

Yes, this bugs me too, seeing as my main is ninety-three years old.

Although the game is guilty of assuming things of player characters in plenty of places, this is clearly not one of them. You're a fledgling hero when Twinshot addresses you, it makes perfect sense for her to call you kiddo. (Mind you, this is still pretty awful and really borderline insulting writing, and actually makes Twinshot a less likeable character than Statesman, but that's beside the point.)

Fortunately, the devs seem like they've started to realize this and have inserted exceptions into dialogue, WWD7 being a good example (Lady Grey casting a spell so you can breathe in space, unless you don't actually need to in which case never mind I guess).

There's an old curmudgeon in Praetoria who calls everyone "Kiddo" too, and I found it less insulting from someone who was obviously an old man himself (and probably called everyone "kiddo") then when Twinshot did it. The further I got in her "story" though, it seemed to me that she may have an association with that old curmudgeon, and it bothered me less at that point.

Saying kiddo is like saying boy. As in "dats mah boy Charname". It doesn't' literally mean you're a kid

Hey, babe, calm down.

No, I'm not saying you're an infant!

Eh, I never took Twinshot's use of "kiddo" as anything more than a playfully affectionate nickname for the rookie on the team, born out of her having been in the military and being used to talking to rookie soldiers that way. It seemed to say more about her personality than anything about my character.

Hey Kiddo

I have to say I agree with the OP. Kiddo does imply age, dispite how people apparently seem to be using it. Regardless, Twinshot, to me at least, comes off as an annoying twit.
But back to the broader point about CoX writting. I do think at times they do tend to over step a bit. Enter a mission and it may tell you that you feel uncomfortable in the confined space. Really? Maybe you had previously decided your character (for whatever reason) loves caves.
So it is one thing to say it is a dark and confined space. It is altogether another thing to tell me how my character feels about it.
This I think is more to the op than a debate over the word kiddo.

I only like being told how I feel when it's a psychic attack.