That's the Catalina I have now.What version of macOS are you currently running? If you aren't at Catalina, you should at least do that upgrade.
That will give you a few more years of usage, but then apps are going to slowly start moving their minimum supported OS beyond Catalina and you'll be stuck without OS and app upgrades for long enough that it'll be time to upgrade.
Your machine is now 10 years old and things have changed dramatically (for the better) in those 10 years and will continue to do so into the future.
So when your machine starts failing you (for whatever reason), upgrade.
No company is going to indefinitely support old hardware and software. With Apple releasing new versions of the OS every year, this is how it is. Also, there is no way to force the upgrade (and even if there is, I wouldn't recommend it).
I intend to keep this computer until it is completely useless, don't want to spend money on things I can still use but I understand you. The battery capacity on my computer is still 95%. Almost never use it without a charger.
It is 10 years old but I have updated it to 16GB of rammine and also changed the hard drive to flash memory. I have a Macbook Air that is 2016 or 2017 and my Pro is significantly better. Pro which I use the most meets all my needs but as you say. When it can no longer be used, I will have to buy a new one. But having to buy a new computer for the actual upgrade when the computer works is too **** much. Same thing with cell phones.