If I have hail damage to my seventeen year old roof shingles and I have replacement cost insurance does my carrier have the right to say that they won't pay due to the age of my roof?

Insurance is a State matter in the United States. Every state has an Insurance Commissioner or its equivalent that can answer your question and if the insurance adjuster is wrong, fix the problem. Shingles should last more than 17 years. You should at the least have 20 year shingles. In this state insurance would probably pay 15%.

I worked for an insurance restoration company ... and in Florida a 17 year old shingle roof is on its way out and usually considered pretty old. However, the insurance company should also consider the condition of your roof and not just its age. If your roof is in poor condition, requires maintenance, and under normal circumstances the hail would not have caused damage....then they will probably deny the claim as "maintenance". But then again, if your roof is in good condition and would have sustained hail damage regardless of its age...then your insurance company should cover the damaged part of the roof and replace the shingles....they probably will not replace the whole roof, just the damaged section.