The most common and most likely answer to this crossword clue is the 10 letter word WORM-EATEN
I've seen this crossword clue in Independent
W
O
R
M
-
E
A
T
E
N
More clues leading to the result WORM-EATEN
Buddy explains!
The straight part
We know that "Old" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case old = worm-eaten.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 WORM-EATEN mean?
WORM-EATEN adjective- Eaten by worms, especially having a worm inside.
- (by extension) Rotten or decrepit.