FB, you're a trouble-maker!
LB, that sounds patronizing to me, also, but into my early 30s I used to have people all the time thinking I was a teenager, asking me, "no school today?" and stuff like that, so maybe she thought you were younger? Still doesn't sound right, but who hasn't put their foot in their mouth from time to time, KWIM? Maybe she meant to pay a compliment and just screwed it all up. Or maybe she's just clueless. If she does it again, just act like she startled you and drop the weight on her foot.