... been mistaken for a boy?

Aside from a mistake in a race where they put me in the 35-39 MALE category, it seems to be happening with greater frequency. Last summer, I was taking a break from work at Del Mar and a security guard came up from behind me and asked, "Are you lost, son?"
I thought is was a fluke. My friends had a good laugh over it. But it has happened more times this year, usually by salespeople.

I don't wear makeup very often (two-a-day workouts put an end to that) and if I have no reason to Dress-to-Impress I'm usually in yoga-type clothes or fitness apparel. I don't wear men's clothes, but I'm not the flowers-n-pink type person, either. I admit I don't exactly have a lot of curves (5-1, size 0), but I'm a 39 y.o. old woman and I'm starting to get a complex.

Am I alone in this?