In my late teens, I think. I always loved ice-cold drinks, and slurping up the mostly-melted slush at the end of my soda...
But crunching began in my late teens. I'd crunch a few cubes in my tea, or grab a cube from the freezer when it was hot out...
And it progressed from there. Now, it's my favourite thing. Give me a cup of ice, and I'm a happy woman!