It certainly sounds like something Lardner would say, but several sources I checked all credit Stengel with that thought, albeit as part of a longer Stengelism:
"Most people my age are dead at the present time. You could look it up."
That said, I can't resist the opportunity to pass along two more of Casey's pearls:
"There comes a time in every man's life, and I've had many of 'em."
"The key to being a good manager is keeping the people who hate me away from those who are still undecided."
If you stop and consider, that's real wisdom, isn't it!