This is going to serve as the main thread for posts of this nature and we will close/merge similar questions into this.
Background
A long long time ago (2.5 years) the Certification system for Ignition was changed to no longer be based on version and to last three years. Certificates are "Core" or "Gold" without a version number attached. This means that any Core or Gold Certification someone has, expires at a certain date.
View Your Cert Expiration Date
You can view your Certificate Expiration date on your IA Account:
account.inductiveautomation.com/tests
The earliest expiration dates are in November 2025.
How to Recertify?
Likely the fastest way is to take the equivalent Certification Test to recertify, or take the next level test if you are prepared.
Acquire the test before your Certification expires, and you will be able to complete it even if the expiration occurs while taking the test.
Completing Gold counts as/resets Core as well, aka you only need to recertify at the highest level.
What if the website is not letting me start a test?
Common reasons you may be unable to start a test include: having a test already in progress, or a website email not being linked correctly. Email training@inductiveautomation.com to verify the status of access for your test/account.
More info on tests?
The links above have all of the info about tests including practice tests. The updated Gold questions are reflected in the currently available Gold practice test 
.