I played with my grandfather earlier this spring - at the Knoll in NJ - good fun.
To give you an idea about his skill level...
A few years ago, we were competing head to head from the same tees, and had several ties - he only has me by about 40+ years. His short game used to beat me like a drum, 1 putt, 1 putt.
The point is, he was much better than any of his peers.
Since some surgery last year, he has begrudgingly moved to the Sr. tees.
At the Knoll they were 6,000, it was too long for him.
If it were my course I'd make them 5,500 max.
The ladies should be 4,800 yards, or at least that's what they were at the Teeth of the Dog. I'm sure Alice had something to say about those.
I'd make the Sr. tees playable for the weaker Sr., and let the better Sr. play from a mixed bag of Sr. and "white" tees.
Lastly,
At Beaumont CC, recently renovated, we put the Sr. tees at 5750. There are a lot of Sr. members. I'll try and get some current feedback if you are interested. They play at sea level.
Mike