Idiom: Old enough to be your mother/father
Jane met a guy who seemed like a perfect match on her favorite internet dating site, so she decided to meet him in person. But when she saw him, he was much older than the picture he had posted! She said she couldn't date someone who was old enough to be her father.
Tina: I heard you're dating someone new?
Jim: Yeah, she's awesome.
Tina: I also heard she's older than you are?
Jim: A bit - she's 36.
Tina: Whoa! She's old enough to be your mother!
Jim: She's not THAT much older. I'm 25.
Tina: Still, 11 years is a big age difference!
Jim: She makes me happy, so that's all that matters.
Meaning: The expression "old enough to be (someone's) mother/father" means that another person is substantially older than the person in question. The expression is used to point out a considerable age difference in dating situations, even when the person is not actually technically old enough to be a person's parent.