After reading Erin's cute joke, I remembered this one.

The husband, 90 years old, had become very frustrated because his wife, also 90 years old, was unwilling to have sex with him.  Finally, he states, "That's it!  I am going out and finding a 20 year old girlfriend!"  The wife replies, "Fine, go ahead, and I will find a 20 year old boyfriend!  But let me remind you of one thing; 20 goes into 90 a lot easier than 90 goes into 20."