Is there a rule for the maximum numbers of darts you can throw in a match of 501 double out game? Like for example two players can't throw out the double in a leg how long can it go on or is there a rule like they have to throw on bull for example after 100 darts thrown or they have to go till one of them makes the winning throw even if it would take for hours.
I have never heard about a limit in darts or visits by the players that would force game shot other than a successful finish.
Looking into the Rule Book of the DRA (Darts Regulation Authority), we find
5.3.4: A Game Shot called by a Referee is valid only if the thrown darts achieve the required finish.
but later on:
5.3.9 The Referee will have the final say in all matters relating to starting and finishing.
This, in my opinion, leaves the referee in a position where he/she can close a leg if necessary. Say, the two players would not want to finish the leg in order to purposely delay the tournament, it seems the referee can decide to close the leg and/or the match and hand the case over to higher authorities.
But speaking for "low level" players who seem to never hit the double, there is no regulation. I've had a horrible leg of darts myself with a truly unskilled player. He finally checked with dart 100-something. Chances are, you will hit the double at some point, even when not aiming. But before, there is no limit.