Every tyre has a build date printed on the sidewall. This is known as the DOT date code. Look for a four-digit number near the DOT letters on the sidewall.
The first two digits are the week of the year it was made.
The last two digits are the year of manufacture.
Use the Smarter Towing Tyre Age Calculator
Find the last 3 or 4 digits after "DOT" on your tyre sidewall. Example: DOT XXXX XXX 4523