1413
"No nation is older than 250"
(lemm.ee)
Transcript
A threads post saying "There has never been another nation ever that has existed much beyond 250 years. Not a single one. America's 250th year is 2025. The next 4 years are gonna be pretty interesting considering everything that's already been said." It has a reply saying "My local pub is older than your country".
Mate, the UK has existed for a touch over 103 years.
The UK of GB and NI is presumably what they're referring to. Whether or not you count changing territory and name as the beginning or end of a nation is subjective, I guess
If changing territory resets the count, then the US is only as old as when Hawaii or Alaska joined (I think Hawaii was the last addition? Dunno, I'm not an American...)
They were both in 1959, but Hawaii was later in the year.