How long are tires good?

I'm working on getting my tractor ready for the road, and I'm wondering if my tires would be safe to use.

The truck has been sitting for about five years.

They must have replaced the front tires on the truck right before I purchased it because they're full tread and there's absolutely no wear pattern and they look like they're brand new. But the age of them concerns me. Should it?

Also how about the rear tires? They are not new tread like the front but they're certainly more than enough to pass inspection and last me for a while.

What do you think?

 

I'll take a closer look tomorrow but I didn't see any dry rot on them at all.

They look perfectly fine to me, but like I said the time the truck has been sitting concerned me.

But if they are okay, that would be great. That much less to put out to get started. I can always buy a new set as I go.