Age of the tire is just part of the equation as to when you replace tires. Heat buildup, low pressure, sun light, sitting for long periods, damage from pot holes, how close to max tire rating vs weight of your MH, and where you live all factor in. Someone on here a few years back posted a gov't study that was very interesting showing tire failures from blow outs being much higher in the southern states due to heat. Everyone's situation is different and some are more risk averse than others so changing tires every 7 years seems comfortable. Some would argue every 5 years is safer and they would be right. I live up north and my tires are always in the shade when parked, I inflate to max pressure, each tire carries the same weight and well below max rating I probably won't replace until 10 years unless I sell the MH first. Tires can be broken down and inspected from the inside for any damage or tread separation.