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What do you mean by "good"? More importantly, what are you trying to achieve?
There have been posters in this forum as young as 12. Many people go to design colleges specifically to learn After Effects.
If you want to work with motion graphics or video compositing, learning After Effects is pretty much essential.
After Effects is a program that can do a simple transition between two still images or produce any composite you have seen in a feature film. The only thing After Effects cannot do is create, edit, and animate 3D models like robots or space ships. You can, however, in concert with a 3D app do anything you have ever seen on the screen and, if you are really creative and talented, probably do something we have not seen yet. You can achieve a successful first project by following these 3 videos: Basic Workflow
It may take years of experimenting and research to create something we have not seen yet. Starting to learn to use After Effects is like having the key to the Snap On truck and access to all the tools. You just have to gain enough knowledge to use them all.