Oil life?? Time vs. mileage ....

same goes for other fluids. I've seen people that change their oil every 2500 miles but never once have the coolant changed, or transmission fluid changed, or differentials serviced. and the big one that nobody does is changing brake fluid.
it should be changed once a year or every 2 years at most. it will absorb and hold water and damage calipers/brake cylinders / lines from the inside out.

they have some red/blue stuff you can use when doing a brake fluid change, you can bleed the whole system out and when it changes color you know you got it all.

engine oil, that's cheap to get a change. 50 bucks or so and worth it once a year on a car you don't drive constantly.