the (approximate) dates that Old English was in use?

OK, off the top of me noggin. Prior to the 12th century, in what is today, the UK. I think Beowulf is a 9th century poem.

After looking at some references: (secundum Vicipediam et cum grano salis) mid-5th to 12th centuries CE. I see that Beowulf is about 700-750 CE. So, I was off on that one.

Ceci n'est pas un seing.