Is it possible to practice pen writing in five days? Can adults practice pen writing in five days?

It's impossible. Whether it's calligraphy or ordinary writing, you want to write well, although genius or understanding does play a very important role.

But diligence and persistence also play a very important role. It is impossible to do it quickly, not to mention that even the most basic word formation can't be understood in five days, let alone the basic skills of various strokes.

There is no shortcut to calligraphy. It is basic to practice calligraphy every day.