Logical AND and OR Operator in shell script

#! /bin/bash

echo Are you young ? ....
read -p "Enter your age : " age

if [ $age -gt 18 ] && [ $age -lt 30 ]
then
    echo You are still young
fi

if [ $age -gt 18 -a $age -lt 30 ]
then
    echo You are still young
fi

if [[ $age -gt 18 && $age -lt 30 ]]
then
    echo You are still young
fi

OR Operation Example :

#! /bin/bash
read -p "Enter your gender : " gender
if [ $gender == male ] || [ $gender == female ]
then
    echo Gender : $gender
else
    echo Invalid Gender
fi

if [ $gender == male -o $gender == female ]
then
    echo Gender : $gender
else
    echo Invalid Gender
fi

if [[ $gender == male || $gender == female ]]
then
    echo Gender : $gender
else
    echo Invalid Gender
fi