It's about mileage, not age. A chain is good for maybe 2000 miles - a commuter might get a year or two out of it, but a courier or serious roadie could wear it out in a matter of weeks. The same basic equation applies to wheel rims, bearings, cassettes, chainrings and (in the case of e-bikes) batteries and motor-gearbox units. If you're changing those parts often enough, eventually something will strip or seize badly enough to write off the frame. Most casual cyclists will never experience it, but an aluminium frame will inevitably succumb to fatigue cracking around the bottom bracket after a few tens of thousands of miles, no matter how well it's cared for.

Three to five years is incredibly good for a bike that's potentially being ridden all day, every day under very harsh conditions.