That's a great question! All our kids are different, especially when it comes to math, so it is hard to put a hard age limit on it.
On the younger end, many kids as low as 5 can play a simplified version that leaves out the Roman Numeral cards and uses only addition and subtraction with numbers 1 to 37. Once the player turns over a couple of cards the other players can help him or her with the arithmetic needed to figure out whether a match is possible.
As your students are ready, add in the Roman Numeral cards, and multiplication and division. The game helps to demonstrate the relationship between multiplication and division.
For more advanced learners, add in squares, cubes, square roots, cube roots, powers of 2, and the Fibonacci series. If you don’t know about the Fibonacci series, don’t worry. The rules explain it, and all game concepts are within the grasp of most middle schoolers even if they haven’t yet been exposed to them at school.
The kids who helped playtest the game range in age from 10 to 15. It is fun for all of them, and there are strategic elements that make the game fun for older teens and adults as well. To level the playing field for the youngest students, you can also introduce a turn timer (not included) to give more advanced players a handicap.
Adults should watch out when playing tweens. Many of them can beat adults because they use arithmetic more than we do. We have become overly dependent on our phones and computers to do our math for us. If that sounds familiar, you may need the game as much or more than your kids do!