My tires are about 5 years old with 44,000 miles. They still have enough tread and only a few hairline cracks in the sidewall. Should they be replace just because of their age?
When the tread is worn down, tires lose traction during braking and won't grip the road well when driving in the rain, ice and snow. But even if there's plenty of tread left, tires should be replaced if they're too old, at least every six years.
Condition is more important than any other detail. Miles will vary from tire to tire more than a complete set. Age will vary because of environmental conditions by tire to tire. Tires of five years old can be borderline if tread condition is even and has enough depth. The 44,000 miles can be different according to the quality when purchased. Did you buy a tire expected to get 60/80 thousand miles? The last thing you mention, which I bet you know is the real telling condition of the tires, is the "few hairline cracks on the sidewall". If you see cracks on the sidewall you might be able to find cracks inside the tread. Would you consider those more dangerous when the tire blows out? Everything about tire use is based on conditions and variable. Cracks in the rubber mean you should get new tires for normal driving. If you do highway speeds get tires now. If you only drove under 35MPH waiting might be OK for awhile. My best bet is you should buy tires now.
There are 2 things working against you. Many tires have an expected lifetime >44K miles, but that is still a lot of heat cycles on the tires, which will decrease grip regardless of tread depth. In the same way, age also decreases the grip of the tire compound regardless of tread depth.
No doubt there are lots of people on the road with older and more worn tires than you have. If you drive conservatively and mostly on dry pavement you can probably get a few more miles out of them. But if it was me, I would replace them.
One more thing. You didn't say what tires they are. If they are high-quality tires (eg, Michelin, Bridgestone), they likely have better grip at this age than lower-quality tires (eg, Westlake).
I would go another year without any worry.
But large cracks or missing chunks of rubber would change that.
If you drive in city all the time, you can use them but on highway, the tires may blow up.
I wonder if they have a good spare. Just in case only one tire is rotten and pops.
Are you sure the tires are five years old? Did you get the date from the date marked on the tire or some other date? Here is how to read tire date of manufacture.