You're using fuzzy math.
Price's birthday is August 26.
Mookie's is October 7.
That's a difference of only 42 days, but you're making it into a full year.
Might as well use exact ages down to the days, if you're going to do a fair comparison.
Edit: Or you can just use the same method Baseball-Reference uses, the player's age at the start of the season.
That makes Price's 2016 season his age 30 season, and Mookie's 2021 season his age 28 season.
2 years difference.