The most common and most likely answer to this crossword clue is the 9 letter word LONG-LOST
I've seen this crossword clue in Financial Times
L
O
N
G
-
L
O
S
T
Buddy explains!
The straight part
We know that "not seen for ages" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case not seen for ages = long-lost.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 LONG-LOST mean?
LONG-LOST adjective- Having been missing or unknown for a long period of time.