How can I find out how old I am on another planet?

You would be the same age wherever you were! I assume, though, what you mean is 'how do you work out your age in, say, Mars years or Jupiter years as opposed to Earth years?'. This is actually quite easy. You just need to know how long it takes each planet to orbit the Sun:

Mercury 0.241 yrs
Venus 0.615 yrs
Earth 1.000 yrs
Mars 1.881 yrs
Jupiter 11.86 yrs
Saturn 29.46 yrs
Uranus 84.01 yrs
Neptune 164.8 yrs
Pluto (dwarf planet) 248.6 yrs

Now what you do is divide your age in Earth years by the length of the planet's year in Earth years to get you age in that planets years.

For example, if I were 21 Earth years old, I would be 21/0.241 = 87 Mercury years old and 21/248.6 = 0.08 Pluto years old.

This page updated on July 18, 2015.