Time dialation as predicted by Einstein is

1/sqrt(1-v^2/c^2)

Given that c is approx 3x10^8 m/s (or about 1.08x10^9 km/hr), then time dilation is approx

1/sqrt(1-v^2/(1.17*10^18))

So at normal speeds, the dilation of time is rather hard to measure.

At 200Km/hr, time dilation is 1 / (1 - 3.429x10^-14) (ish).

So if you spent 20 years working 5 days a week, travelling for 8 hours per day, without holidays, sick, or long service leave, you would age about 5 microseconds less than your stationary spouse.

At 800Km/hr, time dilation is much larger! If you spent the same amount of time in an aircraft cruising at this velocity, you would age almost 1 millisecond less than your train driving brother.

For these reasons, I cannot recommend long duration flights as a method to achieve immortality.