There are no strict rules, but... here’s a tip.
In my experience, apart from the 90% who are doing it for the first time, almost no one updates their headshot regularly, like once a year. Most people only think of it when the time comes.
Time to look for another job.
Here's the hack: update your headshot regularly! Do it at the end of each year or on your birthday. Call it "a gift to yourself" or "marking another trip around the sun."
This way, you'll always be prepared and avoid suspicion ;)