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Jennifer Garner's attitude toward aging is more relaxed than that of Ben Affleck, her husband of five years.

During an appearance on the "Late Show With David Letterman" on Aug. 14, the TV host, 65, asked Garner to verify that she is indeed 40. "Yes, David!" the "Odd Life of Timothy Green" actress responded, laughing. "That's what every woman wants to be asked in this chair! I mean, 'Are you 40?' Why not ask me if I'm 45? 'You look 50!'"

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Letterman then argued that the actress and mother of three (Violet, 6, Seraphina, 3, and Samuel, 7 months) looks like a 20-something, but Garner laughed it off. "I like being 40," she told him. When Letterman asked about Affleck's feelings about being over the hill, Garner said, "It's interesting that you ask that, because my husband turns 40 tomorrow. I get back [to California] around 3, and he's like, 'You're not going to be here in the morning to make my breakfast?'"

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"So he does whine a little bit at the house, huh?" Letterman grinned.

"Well ... I don't know that he's as thrilled with the idea of 40 as I am," Garner continued. "I really like it. I had no problem with it. I feel like, what more could I want? I can't speak for him. But it doesn't look he's as happy as I am about turning 40."

Letterman then probed Garner for a reason as to why Affleck is less enthusiastic. "What's the problem?" he asked. "Is it low T?"

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"Low T as in low testosterone?" Garner questioned before laughing wildly. "Are you asking about Ben Affleck's testosterone level? Really, David! He will thump you. Have you seen my husband lately? He is walking testosterone."