There are no formal prerequisites for this beginner course other then age, 14+.
If you attended an introductory course, have crewed on a boat or are engaged in other water sports all the better.
Swiming skills are desirable, but not required. Still, you should be comfortable on water far from shore.
Unlike dinghy sailing, capsizing is not a 'daily routine' on a keelboat, although a crew member may accidently end up in the water.