Although the physical constraints of age limited the action somewhat in Barnaby Jones, this senior citizen had none of his mental faculties impaired when on a case.
In a pilot that was an episode of the Cannon TV series, Frank Cannon is hired to investigate the death of Hal Jones a colleague. Hal had taken over the detective agency from father Barnaby who decided to retire as senior citizens are wont to do. But his fires are banked with the homicide of his son and Buddy Ebsen and daughter-in-law Lee Meriwether take over the agency with her as Ebsen's secretary. Thus a successful television series was born.
Ebsen was a cagey old bird who a lot of bad guys thought was past his prime. They'd always trip themselves up because they thought he was not really paying attention to what they said. The Medicare set loved Barnaby Jones.
But TV is always after that youth market and after a few seasons Mark Shera was added to the cast as J.R. Jones, a nephew gone into the business with the uncle. Now the rough stuff could be dealt with in house if needed.
Buddy Ebsen as a performer reinvented himself more than Madonna. Over his 95 year life we saw him as musical dancing performer, Georgie Russell companion to Davy Crockett, Jed Clampett of the Beverly Hillbillies, Barnaby Jones, and finally Roy Houston uncle of Matt Houston. And there are a lot more single roles than that, films like Attack and Breakfast At Tiffany's which was a different Ebsen all together from the rest. Was this man ever versatile.