Translation:We are looking for women from twenty to thirty.
As a native British English speaker, I absolutely agree that "We are looking for women from twenty to thirty years" is valid, even if "years of age" would be slightly better. It's kind of frustrating to be marked incorrect for a literal translation that makes sense in English, especially because in other contexts we get marked incorrect for not translating something literally enough.
The default "from twenty to thirty" is fine, and both "from twenty to thirty years old" and "from twenty to thirty years of age" are acceptable alternatives. I would also expect to hear "between twenty and thirty," but that is perhaps not a good translation of the original.
"We are looking for women from 20 to 30" is accepted. However, we have a report that came in at the time of your comment for "We are looking for women BETWEEN 20 AND 30." That may or may not be yours, but it would have been rejected because it is not a translation of the Czech original.