Since today is March 9, 2024, and his birthday falls just two days later, we can calculate his age in two ways:

Considering today's date: If we don't include the days until his birthday, we can calculate his age based on the year:

Current year (2024)  Birth year (1971) = 53 years old.

Considering his upcoming birthday: Since his birthday is very soon, he will be turning 54 years old in just two days.
Therefore, depending on how you consider it, Johnny Knoxville is either 53 years old today or will be turning 54 years old in two days.