Depends on what type tire they are.
I run LT tires on my trailers for 6-8 years or 50k-60k which ever comes first. Michelin for example says;
Q&A... What is the expected service life of tires?
While most tires will need replacement before they achieve 10 years, it is recommended that any tires in service 10 years or more from the date of manufacture, including spare tires, be replaced with new tires as a simple precaution even if such tires appear serviceable and even if they have not reached the legal wear limit.*
ST tires like Carlisle recommends 3-5 years and should be replaced after 5 years.
This doesn't mean how long you had them on a trailer but how old the DOT date number indicates which is stamped in your tires sidewall.
And never over inflate a tire above the sidewall max pressures. I've seen my 16" load E tires at 80 psi on my equipment trailers go to 94-96 psi in 100+ temps and a all day run. This is normal so don't let air out of a hot tire.