Apply it to reality, and things get muddy really quickly.

The major issue is the "private ownership of the means of production". While some argue it's a recent development, others (like me) argue it has been present since the dawn of civilization and, ignoring the "free market" and "voluntary transactions" part, one could argue both feudalism and socialism are capitalistic systems, with the latter often receiving the term "state capitalism", instead.

And then there's the issue of "wage workers". Workers who own their means of production (i.e. freelancers) are still often considered "capitalists" themselves, as under the umbrella of "small capitalists", even if they rely more on their labor than their ownership.