"What is the difference between living and existing"
This is a very deep question... I like it. But, to keep it simple, living is active, while existing is passive. Living is doing, while existing is just being.
It's not the quantity of years you have in life, but the quality of your life. I know people who have lived more in 20 years than those who have been alive for 80. You can exist without really living.
I know that when you look up the words "live" and "exist" in the dictionary, they are synonymous, but when you really think about it, deep down, they are almost exact opposites.
I think, for me, existing is just being alive, breathing, eating, sleeping, and all the stuff humans naturally do. But Living... that's doing what you love, and what makes you happy, and feeling everything you could possibly feel and going on crazy adventures, exploring, learning, discovering things you never thought were possible.
Living is the best thing you can do with your life. My advice: try it.