For me its not sleep , its sore old bones. Once the joints get inflamed , that's it. At one time , that was not an issue , then it became an issue but only after 3 or 4 days of fishing every tide. Now its a few hours then that's it for a few days to a week.
I would say the best combination of experience and physical ability is in your 30's and 40's. I remember when in my 30's I would sometimes go down to south county on a Thursday afternoon and not return until after the monday morning tides. Fish every available oppurtunity with no problem with sleep or decrepidness. I preferred to fish alone since very few could keep up with me and I had no concerns about needing help in case of an emergency. In my 40 I got down to maybe Friday through Sunday night then home to sleep before work on Monday. Time on the rocks didn't really limit me. Then around 45 , you start actually heading out with the idea you will fish x number of hours. may you would say "i can do 6 hours , whats the best places and times to spend the six. Prior to that it just go and fish if there was any hope of catching.
After starting to set a schedule , the hours become less and less. Then you start with the trade off...well I'll fish 9 to midnight but then sleep until intil 5 and hit the morning tide and sunrise. Then its I'll fish the night time or the morning , then its I'll fish the nightime and skip the morning so I can do tomorrow night.
Pretty soon its well I can last 3 or 4 hours then that's it for the week!
Now if the question were , would you rather be young or experienced , all but the biggest fools would choose young!