Update April 2023, 

MacBook Pro and MacBook Air Buyers guide.

We can now instal macOS Ventura 13.3.1 on unsupported Macs from 2012 to 2016, (better to wait till the end of the update cycle 13.6)
Better to do a clean instal and start a fresh and it has to be on an SSD/Flash drive, 

No hard drives and a minimal of 8GB of memory
Time Machine back up all personal data
Erase flash drive
Clean instal of Ventura 13.3.1
Manual migration of personal data and Apple apps only, no 3rd party apps, All apps have to be 64bit
Prices start from $160 no tax

Note if you are running a 2012/2013 and possibly a 2014/2015 that has never had the flash drive replaced and it's already slow or experiencing weird issues you may need a new flash drive, we stock new 1TB NVMe M.2 flash drives with a Sintech adapter.

OR

We can now instal macOS Monterey 12.6.5 (Stable)
On unsupported Macs from 2008 to 2015
Better to do a clean instal and start a fresh and it has to be on an SSD/Flash drive,