Using timespan

[eluser]quindo[/eluser]
I'm using timespan in a test.
I use it to display my age using this command:

Code:

timespan(mktime(5,0,0,3,3,1973),$now);

With the meaning of giving me the difference between the current date and my birthday (3-March-1973).

However, today (24-Feb-2008, 14:32) it gives this output:
35 Years, 1 Day, 9 Hours, 32 Minutes

Somewhere something went wrong.
Anybody any idea what I'm doing wrong?