already

In English, "already" is only used in reference to another situation.

For example:

"Don't forget to do your homework!"

"I've already done my homework!"

"Can you help me with this thing before you go to work?"

"No, I'm already late!"

It is typically not used in general situations like:

 

"Pencils were in use as early as the 16th century."

"Only small amount of toothpaste is needed to clean your teeth." 

Origin of the confusion:

Generally, the German "schon" means "already" in English. However, there are several exceptions.

In German, "schon" is sometimes used instead of "bereits", e.g. "Schon gestern habe ich einen Teller zerstört!", which is in reference to an event today. In English, this would simply be "I dropped a plate yesterday too!" 

In German, "schon" and "only" can sometimes have the same meaning, e.g. "schon kleine Mengen reichen aus".