I bought a 2010 TT about 4 months ago. One of the things I checked was the tires. I suspected they were original and they all checked out to be 7 years old. Tread was excellent so I don't think they saw a lot of road use but the side walls on all were showing signs of cracking. I replaced 5 tires including the spare.
I agree to check the date code on the sidewall, carefully inspect the sidewalls and tread for any cracking. Raise tires off the ground and spin them to check for roundness or sidewall bubbles. Check the air valve for any cracking also.
For my own sense of relief I replace my trailer tires between 7-10 years or sooner if I see any deterioration.