The most common and most likely answer to this crossword clue is the 3 plus 3 plus 7 letter word OLD AGE PENSION
I've seen this crossword clue in Financial Times
O
L
D
A
G
E
P
E
N
S
I
O
N
Buddy explains!
The straight part
We know that "A benefit of one’s golden years" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a benefit of one’s golden years = old age pension.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.