I saw an interview with Irene Ryan somewhere online where she said that Henning didn't think she was old enough to play Granny. But, didn't he want Bea Benaderet to play the part, who was four years younger than Ryan?

I never heard that about Irene Ryan.
As for Bea Benederet though, I heard that when she first saw the script she said "Oh, let me audition for Granny"! He knew she wouldn't get the role since she was too "well-endowed" but let her try out anyway.

The story I've read is that Paul Henning originally had Bea in mind for the role of Granny. Then it was Bea who pointed out Irene Ryan and said to Paul, "There's your Granny."

It was also Bea who later suggested Paul's own daughter, Linda Kaye, for a role as one of the Bradley Sisters on Petticoat Junction. Both of Bea's recommendations turned out to be excellent ones...!

Well, Irene was 60 when she signed to play Granny but she was always "aged" for the show to appear at least well into her 70s and maybe eightyish, kind of like what they did with Estelle Getty in THE GOLDEN GIRLS 20 years later. If Bea had been signed to play Granny she too surely would have been given the "aging" treatment.

You can watch Bea play an old lady in her one and only appearance on I LOVE LUCY which imo was one of the worst episodes of the series. Bea was a very talented actress but I can't imagine her Granny would have been anywhere near as good as Irene's; she might have played her a little too eccentric like the Lucy episode.

Irene wore so much makeup for "Granny" she was often unrecognized on the streets.

Irene appears in normal everyday clothes in a season two episode of 'My Three Sons' called 'Romance of Silver Pines'.

Well it worked out for the best, with Irene as Granny and Bea in the role of Pearl, and later Kate Bradley on Petticoat Junction . My only wish is that she stayed on as Pearl past season 1.

Irene appears in normal everyday clothes in a season two episode of 'My Three Sons' called 'Romance of Silver Pines'.
Yea, Irene had to do some confincing to Pul to let her play the part of Granny by telling him nobody will want to get up that early to come to work, etc... She tied her hair back in abun and acted feisty as all get out> she just blew everybody away and Paul and producer Al Simon immediately said, that's granny.

There I've heard many rumors that Irene Ryan was MUCH younger than she was playing.

I even heard a rumor that Irene Ryan was even younger than Donna Douglas.

Irene wore so much makeup for "Granny" she was often unrecognized on the streets.
Without her "granny" get up she doesn't look like an old person so I guess Pul didn't think of her as Granny or what he was looking for.