Leave the snake alone for a week. Make sure it has a good hide, a small dish of water and put it on newspaper. After a week, put a small pinky in near the entrance to the hide. Then, do not disturb it all night.
By the next morning, if he hasn't eaten it, throw the pink in the freezer and save it for another use.
Like I said earlier, the snake MUST feel secure. Dangling a "flying" pinky is probably scaring the pee out of it. Stop that! LOL! 18 days is nothing to worry about. Try offering food every 5-7 days and once the snake is 6 weeks old, then try more drastic measures.
Offer whole live, whole thawed, or a cut off head. If the snake is hungry, the snake will eat.
I gave a hatchling to a friend of mine. He wouldn't eat for her for the first 2 1/2 weeks he was there. Then, he ate. Now, after 3 feedings, he doesn't even wait for her to put them in his house. She called me a few days ago to tell me that she had two on a napkin, thawing on the table next to his house and when she had him out, he saw them and stole them right off the napkin! LOL!