BASH: IF / ELIF incorrect triggering

I need not just an answer for the following situation, but an explanation please. There are 2 files - NEW and OLD:

touch NEW ; 
touch -t $(date -d '3 week ago' +%Y%m%d%H%M) OLD

Now i'm making the script to output different messages according to the results of comparison of a NEW file to the old one:

#!/bin/bash                                                                                                           
if [[ "$NEW" -ot "$OLD" ]]                                                          
        then echo "file is old"                                                                                       
elif [[ "$NEW" -nt "$OLD" ]]                                                        
        then echo "file is new"                                                                                       
fi

But no matter which condition is correct, "file is old" will always be printed.

The same situation with IF ELSE FI statement.

Where am i wrong?