You can...if you can get all your stuff to still work. Historically, age issues have been about specific software, and often browsers.I intending to stay on 10.15.7 for at least 7 years or until I get a new iMac!!
If you never update software—and don't need to in order to be compatible with newer versions—great. No issue.
When browsers are too old to be supported/updated and are no longer secure, often folks can't do online banking and other security-specific things. When one hits that wall...in the past, there was no easy work-around, other than updating the OS enough to run supported/secure versions of browsers. As an example, Firefox still has support back to 10.12. At some point, that with ratchet up to 10.13, and so on. There are folks out there still running 10.10 and older...and would struggle to have a fully functional browser.
As long as you are aware...don't feel any pressure to update.