Is it normal that i think that i'm not going to get older than 20

Your brain just isn't developed enough to see the future. Planning ahead is not something teens do autonomously, because teens simply see the future as an unknown cloud. You don't have perspective. How could you?

When you reach twenty, you'll see that you still feel like a kitten when you look at the other "adults" around you. When you're 34, you'll see, you'll look at the other parents as if they are more mature than you. When you're 75, you'll see, you still feel like you are growing up.

I'm 22 now, and consider myself a grown woman. I haven't accomplished much. I haven't had kids. I don't own stocks, businesses, a home, a car, or anything. I know from the information imparted to me that...no matter how old you are there is always 'a child' inside, or in other words, something that is becoming. Everyone is always becoming someone based on the small daily choices they make.

What you're talking about is fear of becoming. You are very unsure of who you are, and therefore who you want to be. That's okay. It's so normal! It's part of your development as a human. Not choosing what to do with yourself is also, by the way, a choice.

Motivation is not an object you can get. Motivation is inside of you. It's already there. You already have it. You just have to find the things you like to get it going. It's a lifetime process.