While I wouldn't do the check using root of n but instead the square of the running index since that is faster, he is generally right to just check until the squareroot since every divisor you find already has another factor on the other side of the root you need to multiply with to get n. Think of this as an area of same sice but different side length were you shorten one side so the other get's longer. When you arrive at the perfect square, you don't have to go further since all other sidelengths were already checked "the other way round" (hence add 2 to the output for every divisor except for the root - there the other factor is identical).

You are ${n-m} ${year} old. would be better

why is that?

That's a clever way of concatenating strings

Why -n+m instead of m-n?

Not so beautiful but, anyway...

Codewars could have a button for bad solutions

Why people are voting "Best Practice" to a String concat loop?