I run ST tires 4 years, no matter how they look after 4 years I change them. There is a manufacturing date on the tires, its in code usually 4 digits, the last two digits are the year. The tires could have been a year old when they were put on the trailer. I would replace them if they were mine. Tires degrade from UV and ozone, you can't stop the process.
No man has a good enough memory to be a successful liar. Abraham Lincoln
2016 36FBTS Pinnacle
2016 F350, 6.7, 4x4, DRW, long bed
B & W Companion 5th wheel Hitch