If the tire rubber is cracked to the point you can see "cord" at the base of the crack, for sure replace the tires. Most times the cracking is very minor and only on the surface of the rubber, meaning the tires can go awhile longer.
Turn the front wheels of the car to get a good look at the tread and sidewalls. Get out a good flashlight and really examine the tires. If what you see concerns you take the car to a trusted mechanic, not a tire dealer, for another opinion.
I have 2 cars an SUV, a boat trailer, and a horse trailer. I put relatively low miles on all of them buy spreading the useage around. If I replaced tires every 8 years I'd go broke.
2 years ago I replaced the boat trailer tires that dated back to 1987, they held air fine but had bad cracking and I could see the cord in some areas of the sidewall. I lived with the cracking for a few years because I only used the trailer to store the boat with only 3 miles of low speed driving per year. I replaced the tires to prep the trailer for an 8 hour trip to visit friends using interstate roads. The old tires weren't safe for highway speeds.
On the other vehicles I check the tires but won't change them just on time alone until they are at least 10+ years old. If you do a lot of high speed driving, take your Subaru to "track days" at the local race track, or notice a lot of tire spin on wet roads you may want to replace your tires based on performance.
On a motorcycle I pay much more attention to "dry rot". Since many bikes are ridden few miles per season a 5 year old bike tire can look good, but have "hardened" up to the point where it can slide out when pushed hard in a tight corner. If you have a motorcycle 5 years is time to change out the rubber that meets the road.