How old is a 8-year-old on Mars?

About 4.25 Mars years old

On Earth we count years by Earth's orbit (about 365 days).Mars takes 686.98 Earth days per orbit, so someone who has lived 8 Earth years has completed fewer full orbits — hence a different "age."

A Mars day is only 40 minutes longer than Earth's - but you'll wait 6 months for summer to arrive!