I use just about the oldest supported Mac, and it works great. But it has taken some work to make it great. If you have a slow Mac, it is likely easily fixable!
Here is my step-wise procedure for trying to address a slow Mac:
Common Mac Performance Issues
There are a few common things that greatly slow down your Mac:
- Out of Date software
- Lack of Disk Storage
- Sick Hard Disk Drive
- Slow Hard Drive
- Lack of Memory
- Bad "repair" software
- Restart. There's nothing like a restart to clear out memory.
- Empty Trash, which frees up some disk space.
- Software Update. OS updates and core applications should be kept up to date.
- App Update. Applications and Plug-ins should be kept up to date.
- Disk Utility First Aid/Repair.
- Networking: Restart all networking equipment (wifi router, modem)
- Restart again (restart at least once per week)
- Perform network speed/reliability test (speedtest.net)
- Using Activity Monitor, see what (if any) apps are consuming significant CPU or Memory. Update them, or remove them if reasonable.
- Inspect free disk space. More than 20% free is good, otherwise bad.
- Inspect RAM. 4 GB or more is good, otherwise bad.
- If less than 4 GB of RAM, update to 4 GB or 8 GB.
- If a traditional hard drive is in use, upgrade to an SSD.
- If storage is reported to not be healthy, upgrade SSD.
- Upgrade to the most recent version of MacOS.
- If network is bad, consider upgrading WIFI router to a newer model (anything newer than 2014 should be fine).
Well that's the short list I use, generally from the top down, to address any Mac performance issue. There are some weirder things that can happen that aren't addressed by the above procedure, but I find that to be very rare.
Note that I never install or use any 3rd party utility software - as the vast majority of it does more damage than good.