All fluids do wear out. Brake fluid (hygroscopic) absorbs water over the years and the boiling point lowers. It is Glycol and not petroleum. Moisture in the fluid will form acids and such over time that will attack (swell) rubber seals and hoses. It will also corrode wheel cylinders and calipers.
Taking apart old leaky wheel cylinders, you may find pitting at the bottom of the cylinder bore that provided a leak path. That pitting probably started with moisture in the fluid.
Sometimes stuck caliper pistons get that way from corrosion starting from the inside out. Or if the boot lets in moisture from the outside in.
We change engine oils and occasionally coolant and transmission fluid services, but items like brakes, differentials, transfer cases and power steering are generally forgotten.
How often? I think that at least every 60K miles (96,000km) or when ever it may be convenient like during a pad or shoe replacement or other brake service when the wheels are off.
The hardest (and scariest) part may be cracking the bleeder screws loose. A couple of counter-clockwise 'jerks' or 'batting' the ratchet handle with your open palm helps to get them loose rather than a steadily applied force. I hate breaking off bleeder screws.
Use a 6-point socket and not a 12-point socket that can round off the corners of the screw head. If that happens, your 2nd chance to loosen them is with vise-grips. At that point remove and replace the bleeder screw. Many auto parts stores carry generic ones.
Some have rubber caps over the bleeder fluid hole. Many times these are removed and never reinstalled. They help keep out water and dirt and are important to keep the bleeder hole clear.
Gravity bleeding can be done by just letting the fluid drain out of an open bleeder. Having a helper push the brake pedal is better. With their foot on the brake, open the bleeder, the fluid should spurt and the pedal fall to the floor (another scary sensation). The helper needs to keep it on the floor until you close the bleeder. Then you can signal them with an 'OK' to resume a couple of pumps of the pedal to do it again. Keep this cycle going until the brake fluid runs clear, then move on to the next bleeder.
Brake fluid isn't an oil and should rinse off with water. It can attack asphalt and soften tar, so if you pride your driveway, lay down cardboard or rinse off the spills after the fluid maintenance. The brake fluid can wrinkle the skin on your fingers, so either wear rubber gloves or wash with soap and water afterwards. Have rags handy for this work and use safe jacking and vehicle support practices.
Only choose a fluid that is compatible with your vehicle in your owners manual information. There are many choices. Read the label. I see some advertised as being 'synthetic' and that is OK as long as it is compatible with what is in your vehicle.
DOT 4 is a heavier-duty fluid than DOT 3 and are compatible. It is OK to use DOT 4 in a DOT 3 vehicle, But never use DOT 3 in a DOT 4 vehicle.
Silicone brake fluids (DOT 5) are overkill for most regular vehicle applications and may be OK for racing and heavy-duty applications. It must only be put into a It has no trace of other DOT fluid in it. It has its advantages and is more expensive.