#1 joke - Who is older? #1 joke

I have just read the joke from "Die Laughing" book by William Novak, when I first read it, I can't stop laughing! Hope you enjoy it too!

When Larry's primary-care doctor referred him to a cardiologist, he thought the man's name sounded familiar. And when he showed up for his appointment and noticed the framed diploma on the wall, he recalled that a tall, dark-haired boy with that name had been in his high school class.

But when he met the doctor, he saw that although the names were the same, that was just a coincidence. This balding physician with a wrinkled face was already too old to have been his classmate. 

Even so, he ask the doctor when he had gone to the high school.

"I went to Memorial," the doctor said.

"So did I," said Larry. "And did you graduate in 1964?"

"How did you know?"

"You were in my class!"

"really?" said the doctor. "what did you teach?"

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The lesson for me: Don't judge others!. 

What's your thought of this joke?