54 Years Old
A husband leaves this note for his wife:

"My dear wife - I'm sure you'll understand I've certain needs that your 54 year old body can no longer supply, but I still value you as a wife. Therefore, I'll be spending the evening with my 18 year old secretary, but will be home before midnight."

When the man returns, he finds this note from his wife.

"My dear husband - Thank you for your honesty. I'd like to remind you that you too are 54 years old, so I'll be spending the evening with my 18 year old tennis coach. I'm sure you'll understand that though we're in the same situation, there's one crucial difference: 18 goes into 54 a lot more times than 54 goes into 18. Therefore, I won't be back until tomorrow lunch time.

___Back