**ywtf **any thoughts on the ideas? I really like don’t ask’s “well, someone has to be,” but am interested in your thoughts on my basic comment of holding back to let them share more. ?
I appreciate all the ideas. If I had to pick which one seems the most natural and apropos, I’d go with “well, whaddya know?” “Ain’t that something?” is probably what I’ll try out next time.
As far as holding back and letting them share more, I guess if they volunteer more, then that’s ok. But I’m not all that interested in sussing out their perspective especially if 1) that means prolonging the encounter and 2) they’re fishing for an explanation for my age and rank. Because I mean, really, what’s a person supposed to say to that? I slept my way to the top?
A few times I’ve asked them how old they think I am and usually early 30’s is the response. Then I tell them I’m 40 and they’re like ok, you don’t look like it! And I shrug and say thanks again and try to end the conversation quickly so I can return to my rich inner world. From this I’ve learned I really would prefer to not draw out the exchange longer than is necessary.
Especially if you’re not black.
How about, “No, I’m not”, and firmly change the subject.
“This isn’t actually my uniform, but I did stay at a Holiday Inn Express.”
My response is kinda the same as others here.
“Thanx for noticing.” And move on.
Just as if they said “Hey that shirt looks great on you”… it’s just a compliment.
All good. Yeah, I am assuming that that vast majority who say this are just passing by, but occasionally they may be someone new in your orbit.
If you’re not really super-young for the rank, then I’d also work up some variation of “I’m older than I look”; could be useful if you sense any trace of jealousy or ‘who are you to tell me what to do’ attitude. Being jealous of your youthful looks is better than being jealous of extraordinary promotion.
I’m another baby-faced female: my response to such types of statements is usually just an upbeat, quick “okay…” (which implies “what’s your point?”). Always said with a smile, to make it clear that I’m not offended or annoyed or whatever, but with a touch of faux confusion.
A lot can be communicated with a simple “okay.” 
Aaaaannnnd, there’s your response. “You ought to come check out the painting in my attic.” As a bonus, if you say it with a Mr. Bean grin, they might just contrive to never speak directly to you again…
BTW, I’ve never seen a uniformed member of the USPHS, and supposed that they usually go around in mufti. Except C. Everett Koop, and subsequent Surgeons General.
I seem to recall back around the turn of the century, there was a push to try and get PHS officers to wear their uniforms at work. I didn’t start at HHS until the late '90s, so I can’t say what it was like before that. I do see uniformed PHS officers around the office occasionally now, but there aren’t that many of them in our agency.
I used to look very young for my age and position… and then it caught up with me, and I think I moved to “looks pretty good” for my age.
“Well, I’m damn good at my job.”
**“You’re the youngest person I know at your level/rank/position!” How to respond?
**
“And I’m the best, too!”
Assuming this is something that just started happening, congratulations on your promotion, you with the face! Through the wizardry of utilizing my military experience, the fact that I work on a Navy base in DC, and the information that you’ve revealed in this thread, I will deduce your rank:
You are an O-6.
Am I correct? If so, this is how I’ve deduced it: I’ve seen O-4s as young as 30, and O-5s as young as 35 or so. I’ve never known an O-6 under 40, but I’d presume it’s possible, and most O-6s I’ve known have been 45 or older. Promotion might work differently in the US Public Health Service, but I’d presume that most folks saying this to you are military veterans (or have worked in military offices) and thus would be going by military promotion rates. You could be higher than an O-6, but there can’t be that many flag officers in such a small service, I’m assuming, so O-6 seems like the wiser guess.
Also, do you work in the big giant USDA building? If so, I wonder if you’ve ever bumped into my spouse.
I’m impressed by your detective skills. It is possible I know your spouse.
PM sent!
applause! 
Now tell her how you know her sister is a marine biologist, Sherlock.