would you buy unused tires with a 2018 date code for half price of the same tire new

2008, I might question.  I once set my fastest lap at Race City on a set of A032's that has been out of production for most of a decade.

Are you bright enough to notice cracks in the tread face?

Sure, but only if they had been properly stored and if they were a performance tire that I was going to burn up within the 5 or so years following.  The 5 year limit used by tire manufacturers is great for them, and has resulted in lots of half worn tires hitting the trash heap but I think that it is too conservative, and counting from date in service (i.e. on the car) is one thing, but years in proper storage do not equal years on the road - they deteriorate more slowly in dry, dark storage than they do in service.

I called the Bridgestone tech line a few years ago to ask about tire life and they put me through to a scientist in their research facility. He said that Bridgestone at least is confident their tires will be safe for ten years, because that is as long as they typically track and test tires. He said there is a good chance they will last longer than ten years, but they have no data because it is impossible to know what is happening underneath the rubber without taking a significant number of tires out of service and cutting them apart. Therefore they do not comment on tires more than ten years old.

The above relates to tire manufacture and not abuse, impact damage etc.

I would.

Putting the snows on my truck this year I realized they are 10 years old.  They appear to be in excellent condition, and I don't plan to stop using them

I was going to say, this is GRM.  Of course you should buy it.  I just bought a Jeep that was driving around on tires from the 70s.  I did replace them, but I'm not full send GRM.

A lot of the 5 year thing is to protect people who have no idea what tires are.