The most common and most likely answer to this crossword clue is the 3 plus 4 letter word GET BACK
I've seen this crossword clue in The Sunday Telegraph
G
E
T
B
A
C
K
Buddy explains!
The straight part
We know that "Hit many years ago/exact revenge" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case hit many years ago/exact revenge = get back.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.