The most common and most likely answer to this crossword clue is the 12 letter word GRANDPARENTS
G
R
A
N
D
P
A
R
E
N
T
S
Buddy explains!

The straight part
We know that "older relatives" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case older relatives = grandparents.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does GRANDPARENTS mean?
GRANDPARENTS verb- To be, or act as, a grandfather to.
- To retain discontinued laws or rules for (a thing, person or organization previously affected by them).
- The parent of someone's parent