'The average person' or 'an average person'?

"An average person" is a phrase with an article, adjective, and noun acting normally with each other. It means "any person who can be considered average."

"The average person," as the article "the" implies, is referring to a specific idea that is shared among all people (assuming that's possible) of what an average person must be like. In other words, it's referring to an archetype of the "default" person—the type of person any of us could be if we didn't have any eccentricities or distinguishing characteristics. "The average person" is a common phrase that, taken as a unit, has the described understood meaning.

All that said, the ideas expressed by both sentences are virtually identical.

Use the when you mean something specific. Use a/an when you mean something in general.

In your case, both sentences make sense. I think the difference is that the first example focuses on specific average person, while the second example on a person in general. You may need to refer back to the original context before telling which is better.

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The expression “average person” is a misnomer. People cannot be average. It is people’s quantifiable characteristics which can be described as average, such as average weight, height, age etc.

Instead of saying, “The average American worker earns $12.75 an hour.” It’s preferable to say, “On average American workers earn $12.75 and hour.” The rate of $12.75 is used only as an example.

The songbird is a wonderful animal.

The average person is not.

The article "the" is used to qualify a category.

An average person would not like that. [a=any] The average person would not like that. [general class of persons]

REFERENCE:

Rule 2:

Sometimes ‘the’ is used to generalize a group/whole class.

"the" for a group/whole class

And, isn't it interesting that even here, the the/a idea still follows the basic rule: a in not specific and the is for a specific thing.