Why did my coworker call my other coworker old?

I can't figure this out and it's bothering me. Not sure if it's normal to bother me this much but need some opinions.

So I'm new to where I work, meeting everyone. My coworker is 35. There are two weird guys who work there who she was telling me about. I said, "I think there's a guy called Zack and a guy Brian who I haven't met yet. People keep telling me they're mutes."

Her response was, "Oh yeah, Brian never talks, ever so he is basically a mute and Zack's a weirdo and also barely talks and he's old, he's like 37."

I was like huh? How is that old. I didn't ask her how that's old but I was confused why she said that? One, it didn't seem relevant and two, how is 37 old?

I'm in my twenties, she's 35 (only 2 years younger than him) and she calls herself young, never refers to herself as old, looks younger than her age (looks about 28 to me). So I was confused when she called him old. Unless she meant old as in older?

Since then, I have met them both. Brian is 24, is definitely a mute but looks about 30 to me. Zack actually looks younger than Brian and he's 37.