Is Joan Rivers Too Old To Do Stand-Up?

I went to see Joan Rivers do a stand-up set at The Cutting Room in NYC this week. She spent her time cutting up celebrities ("Michael J. Fox is better in bed now that he has Parkinson's"), herself ("My breasts are so low, I kick them when I walk"), and Sarah Palin ("That baby isn't retarded. He's tired » 11/07/08 1:30pm 11/07/08 1:30pm! That kid…