Exactly this.
My first realization that I must look older than I feel was the time I was on a shuttle bus from one airline terminal to the next on an international business trip, and a 30-something offered me their seat. I don't think these young folk realize that I can still put in 14 hour work days and run to tight connections and lift my own suitcase in the overhead compartment. I don't need their seats, but I guess it was nice of them to ask.
And I HATE the "sweetheart" stuff...when restaurant servers ask, "And what can I get you, young lady?" I want to tell them that in case they hadn't noticed, I'm NOT young, and I'd appreciate being addressed with less condescension.
I used to look younger than my chronological age, but that changed since menopause. My Celtic skin with a bad history of tanning with aluminum foil and baby oil probably doesn't help, and the fact that I have made the choice to go grey.