Old guy tries to pick up 21 year old hot blonde in a hotel lobby bar.
He uses this old line - "Where have you been all my life?".
She fires back - "Well, for the first 2/3 of it I was not born yet"!
Question - How old is the old guy?

which means before her birthday last month the math "almost" worked out.

did you do the math or are you guessing ... what is the answer

2/3 of 63 is 42 not 21 ... nice try but you flunked my class

21 years is 2/3rd of his life she wasnt alive yet  .. so  he has been alive for 1/3 more .. so   21 /  3/2 =    31.5  

If she was born when he was twenty-one, then she'd be about 11 now, not 21.

WRONG....

on the math and everything.  
It's supposed to be a joke.  
What's wrong with you people?

For example, people don't all count the same in every land.

It can even be titillating!

Why did 5 come before 6?

Abbott and Costello; Laurel and Hardy; Martin and Lewis; Bob and Ray; Hope and Crosby; Statler and Waldorf; ... mrfisher and impposter? Are we ready to take this show on the road?