go into the tool bar at the top of the screen

then go to the functions buttons, click on DATE & TIME.
the click on YEAR.

this will then covert a given date in to a serial number e.g the year.

if you click ok then it will return the year 1900, all you have to do now is enter your given date in another cell then enter that cells address into the data bit at the 1900 cell.

do that again for the other cell subtract the cell then you get the amount in years.

if this isn,t enought pm me your address and i will copy a sheet to you.

and the the teacher there a twat