Shellscript If statement returns error

I am trying to check if a file is older than 5 minutes and if that is the case I want to call another shell script which sends me a mail.

check_file.sh:

#!/bin/sh

if [$(( (`date +%s` - `stat -L --format %Y /home/ftp/test.txt`) > (5*60) ))] = 1
        then sh ./testmail.sh
fi

Error output: 3: ./check_file.sh: [1]: not found

Answer

Try something like:

if find /home/ftp/test.txt -mmin +5 &>/dev/null; then
    <your code>
fi