If you had taken your test a year ago, and she had taken it in the last 6 months (for instance), what you just said would still hold.
(, Tue 12 May 2009, 0:49, archived)
The mathematics is even simpler in this case. I'll simplify it down into days for you though...
I passed my test 6,510 days ago, when I was 6,318 days old.
The earliest my daughter could take her test is on her 17th birthday which would make her 6,209 days old.
6,510 - 6,209 = 301 days difference.
(, Tue 12 May 2009, 0:56, archived)