Double check to see if they are affected by a bug with GPS that can affect the time and a few other things with the device as this may cause problems with using them down the line. If not affected then get the most out of them until they become too slow or battery life is too bad for day to day use. If they are affected maybe time for an upgrade.
Apple Support link to information on the issue: https://support.apple.com/en-gb/HT210239Opens a new window
" Starting just before 12:00 a.m. UTC on November 3, 2019,* some iPhone and iPad models introduced in 2012 and earlier will require an iOS update to maintain accurate GPS location and keep the correct date and time. This is due to the GPS time rollover issue that began affecting GPS-enabled products from other manufacturers on April 6, 2019. Affected Apple devices are not impacted until just before 12:00 a.m. UTC on November 3, 2019."