Luigi is Mario's younger twin brother who is pretty much afraid of almost everything, but loves to pitch in and help everyone. Those characteristics define him as an understudy often classified as player 2. Although he's a little taller than Mario, he's a few years younger than him. Because of that statement I almost thought Luigi was older than Mario because he was taller, but I was wrong until I found out Luigi is younger than Mario, his height threw me off lol

Anyway, listen to these voice clips for reference:
https://youtu.be/YAtDVsMqQas