How about Tom Jones?
Born Thomas Jones Woodward on June 7, 1940, Tom began singing at an early age. It wasn't unusual in the Valleys towns of South Wales.
He became frontman for 'Tommy Scott & The Senators' in '63, but his performing clearly went back before that. So a minimum of 40 years, and still going strong.

While we're on the Welsh, how about Shirley Bassey, born Jan 1937 and performing in the clubs of 'Tiger Bay' (Cardiff) by the time she was 15 (so in 1952)

Nigel