(I heard this in a movie and I think it’s pretty cool.)
A man is born in 1955. Today, the 14th of August, 2017, he is 18. How is this possible?
The answer is simply:
1955 is where he was born. So either hospital room number or home address if home birth!
I have heard this one before but I don't remember where, maybe the movie you mentioned.
He was born on an extrasolar planet that revolves around its star in 3.4444444444444 Earth years.
"Today, he is 18." Which means his name is 18. Or he is in jail, having number 18.
The man died in 1973 and thus only lived 18 years?
At the risk of giving the obvious answer(s),
or, almost equivalently,
- He’s been in suspended animation / stasis for 44 years.
- He’s been travelling in space for $n+44$ years at such (relativistic) high speed that only $n$ years have passed for him during his trip, so he’s aged only $n$ years. (And he’s spent only $18-n$ years on Earth.)
The person was in space or another planet. People age differently in space/other planets.
This man acted in interstellar movie maybe.