The first translation is indeed incorrect, but not for the reason you would assume. The word "Kari" which means a rock at sea is also a common man's name in Finland. So the translation would be "Kari has 3 children, the product of whose ages is 455. How old are the children!"
The mathematical problem is indeed a little hard, but not impossible. A possible example is 5x7x13. (I divided 455 by 5 since it could very well be a factor, and considered what numbers would make up 91, which is needed to get 455 from 5.)
I hope this helps!