Hard to tell form the responses but there is an answer to the question.
The only lgal limit I've seen in my limited experience applied to scheduled airline service, which very few helicopter operations are. I believe those limits are in the 60 to 65 year bracket.
Recently in Nigeria, there have been a number of guys laid off in response to customer pressure to limit the pilot age to 58 (now with a near-term target of 54 as a max.
Otherwise, just keep a medical and put up with the endless semi-annual intrusions.
I admit the answers aren't all that precise and they may have errors in my memory, but I don't have any paper in front of me right now to confirm things. Pulled it from my memory.