Brake fluid does eventually go bad, but not for a very long time. I have seen brake fluid that had turned to solid granules. This was usually in something very old that may have set exposed to air and moisture for 20 years or more. Something old enough that that it didn't have a modern DOT 3 or better fluid in it. When I worked in the brake shop, with many older, poorly maintained vehicles, I never remember replacing the fluid alone as fixing any problem or heard anyone suggest it would prevent problems.
Starting out new and kept sealed, the brake fluid will outlast the other brake components except for the actual castings. Whether you follow the good practice of rebuilding/replacing every lining change, or only every few changes, the fluid will all be replaced long before it would go bad. Leave the calipers go until they start to leak, and you are asking for problems. In that case, you may as well start with a rebuilt caliper. If and when you you get the piston out, likely it will be corroded and need to be replaced, running the price of the job at least near if not over the price of a rebuilt one. A corroded piston that was forced back into the caliper, may not pop out with a shot of air. At the brake shop, we had a bench set up the more difficult pistons yielded to. I have heard of people using adapters to fit a Zerk fitting and using a grease gun to extract pistons. Yeah, there are tools made for the job, and they do work on ones that aren't too bad.
At 13 years old, take a close look at the hoses and lines. If the hoses look like old, OEM ones or just old, replace them. Don't forget the one to the rear brakes. Look at the steel lines. Pay particular attention to the hardest to see places. That is where crud collects and rusts the line. I don't remember any of the many brake lines I replaced, looking like they rusted from the inside. Often you could hardly see where it was leaking for all the rust and crud on the line.
Any time you replace lining, clean up all the hardware and replace any that isn't like new. Replace all springs and O-rings. I use graphite on metal to metal moving surfaces and silicone grease on rubber on metal to rubber, internal and external. Bleed screws get silicone. Your shoes and calipers must be free to move to apply and release the brakes. This makes a real difference, not an imaginary one.