Take In A Boarder

An elderly man tells the Doctor he is planning on marrying a women of 30, and would he have any suggestions.

- Yes - says the Doctor.

- I would advise you to take in a boarder.

A year later at his 80th year check-up, the Doctor asks how everything is going. He says fine his wife is pregnant.

The Doctor remarks:

- so you took my advise and took in a boarder?

- Yes I did, is the reply, and she's pregnant also.....