5yr/60K interval seems to be pretty common on most 9th gen owners. So far, I've only changed the "pink" stuff once in my cars that have that as the factory fill, and that was roughly around the 5 year mark on the Matrix. The Rav4 is still running with the factory coolant fill in it.
Chemical testing with strips is pretty easy to do, but unfortunately, not a perfect way to check the coolant. Most only test pH - which can be misleading in some cases. Same goes to those specific gravity liquid testers - only shows you the freezing protection, nothing about the chemistry.
You can test them by sending them to a lab - usually those used oil analysis centers can also test coolant, but those tests can get pretty expensive. For me - it was cheaper/less work to stick to a very conservative change interval. Because of the amount of miles that I can quickly put onto a car (~20K-25K yearly), I choose intervals that works for me - this may not be the case for everyone.
That said - my 8th gen Corolla sees Toyota Red + distilled water changed every 2 years (very conservative - probably can push this out to 5 years and still be OK), Matrix got changed at 5 years as a test (again very conservative - plan to push this back a couple of years), Rav4 hasn't gotten changed yet - but my plan will be still change it at around the 6 year mark to baseline it and then monitor it over time, this will likely be the same way as the Matrix - the next time might be 7-8 years easily, if they both act the same after changing out the factory fill.