My Firestone FS561's were manufactured the 19th week of 2017 and they are on a low milage Class A. After reading the materials on the Firestone website (the Data Book), I didn't find any information about recommended replacement due to age. They have an enhanced casing warranty until 6.5 years after mfg so that may be a clue. Weather/ozone cracking after 4 years from date of tire manufacture, regardless of date of purchase is not covered. Normal warranty is 6 years. I'm hoping that these are a 10 year tire. No visible ozone aging. Does anyone have the recommended replacement schedule for these tires? Thanks