The most common and most likely answer to this crossword clue is the 6 letter word INCEPT
I
N
C
E
P
T
More clues leading to the result INCEPT
Buddy explains!

The straight part
We know that "The old begin" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case the old begin = incept.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 INCEPT mean?
INCEPT verb- To take in or ingest.
- To begin.
- To begin a Master of Arts degree at a university.