Actually 6 MONTHS (not weeks) is when most cats get spayed/neutered. But 5 is not old! She should have no more complications than a youngster. And, her uterus would be easier for a vet to locate than the small organ on a half grown cat.

The only time I think age would be a factor is in an ELDERLY cat where the anesthsia would be a concern.

So, I would highly suggest getting the spay done now so that other complications (cancer of the uterous/cervix/ovaries..and other risks) don't have time to occur.