Cash, who still presents shows on BBC radio in the South, played his first record, Bill Haley and His Comets' Rock Around the Clock, in Canada.
"This little job came up as holiday relief on 15 August 1964," he said.
"It feels more like 50 minutes than 50 years. There were times when things weren't the best in the west, but 99.99% of the time they were great."
Cash, aged 72, was born in London but went to Canada with the Merchant Navy.
His first broadcast give him an audition tape to take to the pirate ships broadcasting offshore to Britain, and he joined Radio London.
"I saw this guy huddling over and being very ill, because the ship was going up and down at a heck of a pace," he said.
"He said, 'I'm Maurice Cole - they call me Kenny Everett'."
When the pirates, which inspired the 2009 film The Boat That Rocked, were outlawed, Cash became one of the first DJs on Radio 1 in 1967 alongside the likes of Tony Blackburn, Pete Murray, Ed Stewart and John Peel.
He also worked for Capital Radio for 20 years from 1973 before rejoining the BBC in 1999.
"I love talking to the people and getting their reaction," he said. "And, of course, you get to play the best music on the planet, which can't be bad."
Cash's shows are broadcast at weekends in Kent - where he lives - Surrey, Sussex, Berkshire, Dorset, Oxfordshire and Hampshire.
There will be a special show on 25 August, but he said he was spending the 50th anniversary of his first show getting an MOT for his car.
"Maybe I'll have a cup of coffee or something later on with the wife."
Former pirate radio and Radio One DJ Dave Cash is celebrating 50 years of broadcasting.