a laptop can last longer than 3 years, the problem is usually in about 3 years there will be software which your computer will run very slowly if using, and there isn’t much of an ability to upgrade the speed of a laptop like there is with a desktop, however if you never need to install new software or upgrade your current software you can use your laptop till it breaks physically, this isn’t really how people use computers these days, usually people are always updating and installing new things