I don't think there is any "protocol" really. It's pretty typical "small talk." She was just trying to get to know you.
Don't think it had anything to do with her age.
I don't find anything inappropriate about it. Just tell her "No, I don't." if that's true.
I was really thin when I was young. People used to say, "Man, are you ever thin! You should eat more!" Little did they know I ate more than anyone I knew. I didn't like those comments at all, and found them really inappropriate.
Would those same people say, "Man are you fat! You should eat less!"?
"Do you play basketball?" is a pretty harmless question. Though being the brunt of questions pertaining to height, if you are really, REALLY tall, could be just as tiresome as hearing comments pertaining to weight I suppose.
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I'm not likely to be around much longer. As before when I first signed up here years ago, I'm finding that after a long hiatus, and after only a few days back on here, I'm spending way too much time here again already. So I'm requesting my account be locked, banned or whatever. It's just time. Until then, well, I dunno...