While Jimmy Young was certainly a singer before becoming a DJ (Unchained Melody was probably his biggest hit), I can't find any record of him recording The Twelfth Of Never. It was a hit in the 50s for Johnny Mathis and the 70s for Donny Osmond, and has also been recorded by Elvis Presley and Olivia Newton-John among others, but I can't find any reference to JY having a bash at it.
Another of his Big hits was:- "The Man From Laramie" (1955) His recordings have been re-released on the Vocalion label and EMI Gold. I haven't found the track "The Twelve of Never" listed.