It’s all very arbitrary and depends on the definition of computer for the individual.
Ultimately it does, I think, come down to practicality. Can I still use this thing to get what I need to do done, and can I still do it securely?
The security part can be more or less important depending on computer, as well. If you’re a Mac person, your machine may be obsolete as soon as Apple decides to stop giving you security updates. If you’re a Linux person, you can probably maintain a secure system easily on 10-15 year old hardware.