A roof near end of useful life will likely result in a major claim. They are not going to accept a third party opinion, nor should they. They are on the hook, not an inspector. No one can precisely predict when it will fail, too many variables so they will be conservative.
InterNACHI's Estimated Life Expectancy Chart for Florida Homes
Asphalt Shingles (3-tab)
10 to 12
Asphalt (architectural) 15 to 20
However, keep in mind that the harsh climate in Florida, including hurricanes, heavy rain, high humidity, and intense sun exposure, can cause wear and tear on roofs and shorten their lifespan