grandparent

(one) could be (someone's) (parent/grandparent)

One is old enough to be someone else's parent or grandparent. Used in reference to two people who are or may become romantic or sexual partners, especially to indicate that the speaker thinks such a pairing would be inappropriate. He's going out with Mary from the legal department? But she could be his mother! I don't feel comfortable with this. I could be your grandfather, for heaven's sake!
See also: could

(one) is old enough to be (someone's) (parent/grandparent)

One is old enough to be someone else's parent or grandparent. Used in reference to two people who are or may become romantic or sexual partners, especially to indicate that the speaker thinks such a pairing would be inappropriate. He's going out with Mary from the legal department? But she's old enough to be his mother! I don't feel comfortable with this. I'm old enough to be your grandfather, for heaven's sake!
See also: enough, old
Farlex Dictionary of Idioms.
See also:
  • (one) could be (someone's) (parent/grandparent)
  • (one) is old enough to be (someone's) (parent/grandparent)
  • grandfather
  • parent
  • empathize
  • empathize with
  • empathize with (someone or something)
  • come over
  • ride on (one's) coattails
  • ride on coattails