The most common and most likely answer to this crossword clue is the 7 plus 2 plus 1 plus 3 letter word GETTING ON A BIT
I've seen this crossword clue in The Guardian
G
E
T
T
I
N
G
O
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A
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T
More clues leading to the result GETTING ON A BIT
Buddy explains!
The straight part
We know that "Elderly/compatible to some extent" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case elderly/compatible to some extent = getting on a bit.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.