She pointed out that Crowe, 50, had actually been making a point about himself.
Streep said: "The journalist asks him, 'Why don't you do another Gladiator? Everyone would love that'.
"He said, 'I'm too old, I can't be the gladiator any more, I'm playing parts that are appropriate to my age'.
"The conversation went onto actresses, so that was proving a point that he was talking about himself, as most actors do."
She said she had actually been offered roles as witches when she entered her 40s but turned them down because they did not feel suitable at the time.
But the 65-year-old said she was happy to accept this time around.
"Why this witch? Well I thought: age appropriate," Streep said.
"I felt it was time, and it was not time at 40. Also, I just had a political sort of reaction against the concept of witches, of old women being demonised into age being this horrifying scary thing.
"I just didn't like that. I didn't like it when I was a little girl and I don't like it now.
-AAP