I can see why there is some conflicting advice. I had an unspayed female with til 8-9yrs who then had to be ots from uterine cancer. I then had a rescue female spayed at 4-5yrs, she was full of tumours when they opened her up, she then had to have another operation with 4 months to remove a lump under her skin then died unexpectedly, without symptoms, around 2 months later.
I think spaying as early as possible is the key..... and any deaths after a spay could be due to something going on inside, the op 'triggers' or cancers which have unknowingly spread, of the fact that some older buns just dont seem to cope as well. Valerie was spayed last Thursday at, shes not quite 6 mths, and I would always definately spay a female where possible.