What factors does a judge use in determining when to strike a strike?

There is not a single factor, but length of time between a previous strike and the current offense is one. This only comes into play when there is a current offense. A judge does not simply strike an offense from the record after the passage of time. People vs Romero is a case that allows a judge to strike any past convictions and sentence the defendant to less time in jail than a normal Three Strikes conviction might call for. This does not mean that the felony conviction will disappear from your record. Consult an attorney for more specific guidance.