Generally speaking, if the strike prior happened a long time ago, if the accused has had a clean record since then, if the strike prior was less serious, and if it wasn't too similar to the current charge, you have a better chance of having your Romero motion granted. A lot depends on the individual judge.
Your fiance's lawyer will be able to tell you about it.
The short answer is that the "qualification" for the granting of a Romero motion is whatever will convince the judge that striking the strike is in the interest of justice.
Five years is close in time, but it's not the final analysis. What was the strike for? How much time did he do? What has he been up to since that crime and this one? Are the strike and the current offense related? Is the new case non-violent?
There are many factors that go into a Romero motion - each one is unique and depends on the facts and individual involved. Your fiance should be discussing this with his attorney... and if he doesn't have one, he sure needs one.
It's not clear from your question whether your fiance is, in fact, facing a new charge in which the strike prior is alleged, or if you are inquiring whether a strike prior can ever be permanently removed from your finance's record via a Romero motion. The former has been correctly addressed by the previous posts. If, however, you were seeking an answer to the latter scenario, the answer is no.
Once a strike is on your record you cannot prevent it from ever being used in any future case, unless you are able to get the conviction reversed or vacated on independent grounds. A Romero motion only applies when someone is charged with a new felony and they are trying to get the court to strike the prior for sentencing purposes on the new case. If the judge decides to strike the prior under Romero, it does not prevent the strike from being used against your fiance in a subsequent case. The strike still remains on his record.