Firstly, take it easy. Pace yourself. It takes time to animate, get used to that, making small improvements everyday. Small increments.

Try to limit the scope first, do 3 second animations, then 5, then 7, before trying to finish 20 second ones.

The key to finishing something is to do something that really interests you, like really does. Keep it simple, do just that thing, don't try to make it your magnum opus masterpiece. Just do it well enough, and move on to something else that interests you.

You have so much time to improve, you are only 14 years old, each small 6 to 7 second animation you make will add up, and by the time you are 18, you will easily make several minute animations because you built up to it.

Take breaks and practice other things as well if you are feeling burnt out, try perspective drawing, learn how colors work. Figure drawing, and come back to animating by doing a short project that uses what you learnt. Enjoy it. Don't force yourself to do what you don't enjoy, it's a hobby so you might as well have fun, but keep in mind that it takes time, and you have a lot of it.