I agree that you're never too old for Santa. I could see the grinchette's point, to an extent, and I would have understood if she'd said nicely that they had limited time and would prefer to use that time for children who actually believe in Santa, but her presentation was extremely rude. However, I would never fault you for asking, and I think it was a fun and thoughtful idea. Either way, you probably could have taken the photo and gotten out of the way in the time it took for her to go on her little tirade, so her argument doesn't completely hold water for me. You aren't 4, so you don't have to be coaxed onto Santa's lap, asked what you want for Christmas, and all that. You simply wanted 10 seconds to take a photo, I don't think that's unreasonable.
I hope you were able to get a cute picture to send your family!