The most common and most likely answer to this crossword clue is the 6 letter word STAGER
I've seen this crossword clue in The Daily Telegraph
S
T
A
G
E
R
More clues leading to the result STAGER
- Male leading Queen, an experienced performer
- Horse and dog in residence rejected
- Old actor to move unsteadily, losing heart
- Old actor‘s theatrical entry point?
- Old actor, getting wiser over time
- Deer with royal putting on performance
- Veteran in shock losing heart
- An old one will be experienced — in the theatre?
- An old hand, one putting on a show
- Old actor’s unsteady walk, losing heart
Buddy explains!

The straight part
We know that "An old one will be experienced — in the theatre" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case an old one will be experienced — in the theatre = stager.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 STAGER mean?
STAGER noun- An actor on the stage.
- One who stages a theatrical performance.
- One who has long acted on the stage of life; a practitioner; a person of experience, or of skill derived from long experience.
- A horse used in drawing a stagecoach.