Manufacturer lifespans assume a pool that gets a winter off. Ours don't. Equipment here runs close to year-round, in heat, humidity, and in coastal neighborhoods a constant film of salt air, so it's fair to expect real-world life at the shorter end of every published range.
Pumps are the workhorse and the most common replacement. A single-speed pump run daily gives you years rather than decades, and the failure is usually a seal, a bearing, or an impeller rather than the whole unit. That distinction is worth insisting on, because a shaft seal is a modest repair and a new pump is not. When a pump genuinely is finished, a variable-speed replacement is worth costing out, because running filtration slowly for longer uses dramatically less electricity than running it fast for a few hours.
Filters last longer than pumps but the media inside doesn't. Cartridges soften and stop filtering finely long before they look ruined. Sand rounds off and channels. DE grids tear. A filter that needs cleaning every couple of weeks instead of every couple of months is telling you the media is done, not that you have a dirty pool.
Heaters and heat pumps are the equipment most affected by where you live. Near the coast, corrosion attacks the cabinet and internals from the outside, and a heater a mile inland will simply outlast the same unit near the water. Salt cells are consumables with a defined life measured in operating hours, and they degrade gradually rather than failing outright, so output falls off quietly while you assume the pool is being sanitized.
The signs worth acting on are mostly cheap to catch. New noise from the pump. Air in the pump basket, which means a suction-side leak. Filter pressure that climbs faster than it used to. Water that needs more chlorine than it did last year to hold the same reading. None of those are emergencies on the day you notice them, and all of them cost more the longer they're left.