"Mes grands-parents sont jeunes !"

Translation: My grandparents are young!

[Chantastic92]

Why does "grands" agree with the plural "parents" here, but if you're talking about a grandmother, the word isn't "grande-mère" (with "grand" agreeing with the feminine "mère")?

[DianaM]

It's not even "grands-mères", although it is "grands-pères". I try not to get too exercised about weird grammar rules in any language but I have to say, that one is particularly puzzling.

[Ben261532]

Even younger than me!