We reduce option fees from the standard $75 because of their age, or because they have special needs.
For ferrets that are otherwise happy and healthy, the adoption fee for ferrets over 4.5 years is $50. For ferrets over 5.5 years, the adoption fee is $40. Ferrets of these ages are still quite energetic - many people cannot tell the difference between a 3.5 year old ferret and one that is 6 years old if it's had good care.
It's not uncommon for ferrets that receive a premium diet and have their medical needs cared for (adrenal surgery, etc) to live over 8 years - our last 3 'pet store' ferrets each passed-away at 9.5 years of age.
Besides age, fees are reduced for ferrets with unique needs (even for ferrets!), the discount will be on a case-by-case basis. Examples of these 'unique needs' would be a medication regmimen, special diet, etc. In these cases we will be more selective in our pre-adoption interview and our expectations will be a bit more specific.