can u teach an old dog new tricks

sorry, no. once a Mac is no longer eligible for macOS upgrades, there is nothing that can be done to make it eligible again.

but even so, if the Mac is still working good for you, you can of course keep using it. I have a 2009 MBP that I use for some light usage when I want portability. it works just fine for that.

If the user whats the latest and greatest versions of macOS,  all is not lost.

Explore the Apple Trade-In  Process where the Value of the exiting device could be used against the cost of a new Apple Computer, iPhone or iPad 

Notation - Some devices, depending on the computers age may have little to no value at Trade In time.

But at least the device will not arrive to the Land File Site and be recycled in a responsible way by Apple

Or Shop Refurbished Apple computers at an Apple Reduced Cost

Have used both previously and have been satisfied each time.

Jeffrey is correct. High Sierra 10.13.6 is the latest version of macOS Apple supports on a 17" Late-2011 MacBook Pro.

As far as "all is not lost", you can also purchase a new Mac if you want.

Refurbished units from Apple work just as good as New Machines and do have the same Warranty as a New Computer.

Yes they maybe a older model but Apple is often times offer some pretty new units

The Laptops I have purchased even had Brand New Batteries installed

Reduced costs by Apple Standards lol and just as good IMHO

You know what they say about opinions… 😎

In any case, refurbs are not the only option.