I'm 33 and I still do it when I'm really excited. I just tell people I'm gesticulating wildly on account of being 1/4 Italian!
My Dad was 58 and still flapped his hands when he was very happy or angry or had an emphatic point to make. No one thought anything of it-- they just thought he was a very passionate speaker!
I would very much like to get rid of the urge to bang my forehead against walls when anticipating something stressful, though. I do it very gently but it still freaks people out. I try very hard to substitute pacing for head-banging. That bugs them too, but not nearly as much.
Sitting in the psych room in the ER, I pulled out all my eyebrows because the room was too small to pace and I knew banging my head against the wall would get me sedated in a hurry. It took six weeks for the eyebrows to grow back but did not upset anyone-- tapping my head against the wall would have done no damage whatever but would have had all the staff in an uproar.
Sometimes NTs make NO SENSE.
Moral of the story-- Stim and smile, and f**k 'em if they can't take a joke. A few years out of adolescence, anyone with any sense will have more important things than a little hand-flapping to worry about. Just try not to do it on a crowded bus, lol. Hope you can work out a more space-efficient stim for crowded places. I like hair twirling, finger-wiggling, head-bobbing, and bouncing on the balls of my feet.
Hair-twirling's innocent-- for girl anyway. I can pass the rest of them off as "too much coffee."
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"Alas, our dried voices when we whisper together are quiet and meaningless, as wind in dry grass, or rats' feet over broken glass in our dry cellar." --TS Eliot, "The Hollow Men"