If a human average life span is 60-80 years on earth, on mars will the average life span of a human be 62-82 years of earth years? Or will it be 60-80 years of Mars years?
Relativity is about the relative state of the thing observing and the thing they observe.
Locally (e.g. on Mars) things do not go slower for you, but someone observing (e.g. from Earth) sees time passing more slowly for you.
Locally your life on Mars is not lengthened. Measured from Earth, more time will pass on Earth (as measured by someone local to Earth) than passes on Mars (as measured by someone on Earth observing Mars).
This is more complicated than it might seem at first glance because it works both ways. You (on Mars) see me (on Earth) moving, so from your point of view you also see my time frame slow down relative to yours. From an everyday human point of view that seems like a paradox, as we would not expect both of us to see the other's person's time pass more slowly than ours, but relativity does work that way.
There's a question (or two) on Physics SE dealing with the "why" that happens and why it's not a mistake or a fault with the theory. Here is one.
It's even more complex when you have planets in orbits around a star, because that uses General Relativity and there are even more subtleties and additional effects on the rate of time we each measure for the other. Gravitational time dilation does not work both ways - that depends on the strength of the gravitational field (from everything) so it's different for each observer. Wikipedia's Time Dilation page is a reasonable place to start reading from, I think. Note that general relativity is considerably more complex mathematically than special relativity.
We have measured these effects - they are real, but very small in human experience of them.
