lol dat bad lip reading meme
Since the "can" in "You can eat sand young man" is imperative/instructional rather than ability, a more natural way to say it is
砂を食べるがよい。 Or more vulgarly,
砂でも食べてろ。
I never knew that. I believed that "can" is just equal to "be able to" and the one can be replaced with the other.
Thank you very much for your instruction.
In any case, we cannot eat sand.