A Facebook post claims that “due to changes in validity since leaving Europe, your passport is now only valid for 10 years from the issue date on your passport.”
Historically, when you renewed your passport as an adult, it was valid for ten years from the date your old passport expired. So if you renewed it early, that meant your passport might have an expiry date more than ten years after it was issued. (In 2018 the rule changed so new passports are now valid for ten years since they were issued.)
However, now the UK is not an EU member, your passport must be less than ten years old at the point at which you leave most countries in Europe. (Passport requirements vary in other parts of the world, and details can be found on the Foreign, Commonwealth & Development Office website.)
The post also says: “Most countries in the EU require that your passport is valid for 6 months on the date of return from your holiday” and that for some countries it is three months.
The UK government actually says that most European countries require you to have at least three months left on your passport on the day after you leave, not six months. This is also what the EU’s website says.
The UK government therefore recommends that you have six months left on your passport when you enter a European country, as this allows for you to travel for three months as per normal rules on visiting most of Europe without a visa, to make sure you have the required three months left on your passport when you return.
As the post notes, you can check your passport’s validity for travel to Europe on the government’s website.