If, Elif, Else

#!/bin/bash
read -p "Enter your Age: " AGE
if [ $AGE -ge 80 ]
then
    echo "You are very old"
elif [ $AGE -ge 40 ]
then
    echo "You are old"
elif [ $marks -le 18 ]
then
    echo "You are very young"
elif [ $marks -le 30 ]
then
    echo "You are young"
else
    echo "You are the Rest"
if