How old is the United Kingdom (U.K)?

That depends on what you mean by "the United Kingdom."

• The modern United Kingdom, in its current form, dates from 1927, when its official name became the United Kingdom of Great Britain and Northern Ireland after most of Ireland left the union. As of today (July 2026), it is 99 years old.
• The state commonly recognized as the United Kingdom was first created on 1 January 1801, when the Kingdom of Great Britain and the Kingdom of Ireland united to form the United Kingdom of Great Britain and Ireland. By that definition, it is 225 years old.
• Before that, the Kingdom of Great Britain was formed in 1707 by the union of the Kingdom of England (which included Wales) and the Kingdom of Scotland.