Time is indeed relative. The lower the effect of gravity the faster time travels.
Scientists built two incredibly accurate atomic clocks and were able to validate Einteins theory by showing that time does travel faster on the higher altitude clock even if the clock only differ in altitude by a few feet.
http://www.independent.co.uk/news/scien ... 88195.html
So just think...
- Your head ages faster than your feet.
- The higher you live above sea-level the faster you age.
We're only talking a few minutes at most over 80 years (relative to sea level) but the theory has been prooven.