I’m guessing 10-12 years is more appropriate for trailers in commercial service with daily hard use.
With small molded trailers, 20 years or more is common. One issue is deterioration tends to be so gradual it doesn’t get noticed. I have yet to hear of anyone replacing a 20+ year old axle that didn’t report a marked improvement in ride quality.
Storing the trailer on jacks may help slow the gradual sag in ride height, but it doesn’t prevent wear from use and abuse (potholes, curbs, rocks…) nor the gradual deterioration of the rubber cords as they age.
Absent any indications of a problem (unusual tire wear, excessive bouncing, or rubbing in the wheel wells), around 15 years is a good time to evaluate the axle condition of your small molded trailer, and periodically thereafter.
A loud squeak sounds more like a leaf spring axle issue. If you have a torsion axle I’d be looking at brakes
, bearings, coupler, anything that moves.