Conoce tu edad con un programa en bash

En este programa tu vas a insertar tu nombre, año, mes y día de nacimiento, para que de esta manera te diga cuantos años tienes y cuantos meses. Aquí esta el código:

#!/bin/bash

currentYear=$(date +%Y)
currentMonth=$(date +%m)
currentDay=$(date +%d)

echo "What is your name?"
read name
echo "What is the year of your birth?"
read birthYear
echo "What is the month of your birth?"
read birthMonth
echo "What is the day of your birth?"
read birthDay

yearsOld=$((currentYear-birthYear))
age=0

if (( $currentMonth >= $birthMonth )); then
        if (( $currentDay >= $birthDay )); then
                let age=$yearsOld
                echo "$name, you are $age years old"
        else
                let age=$(( yearsOld-1 ))
                echo "$name, you are $age years old"
        fi
else
        let age=$(( yearsOld-1 ))
        echo "$name, you are $age years old"
fi

months=0

if (( $yearsOld==$age )); then
        let months=$(( currentMonth-birthMonth ))
        echo "With $months month(s)"
else
        let months=$(( 12-birthMonth ))
        let months+=$currentMonth
        echo "With $months month(s)"
fi

if (( $currentDay >= $birthDay )); then
        echo "With $months month(s)"
        if (( $currentDay == $birthDay )); then
                echo "With 0 days"
        else
                echo "With $(( currentDay-birthDay )) days"
        fi
else
        echo "With $(( months-1)) month(s)"
        echo "With $currentDay days"
fi