If all you need is the amount of full years (the age) in OpenOffice.org only, =YEARS(start;end;0) will suffice.
My sheet demonstrates how to deal with time units and intervals in a compatible manner, using functions that are common in all spreadsheet applications such as Excel.
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and add "[Solved]" to the subject line if your problem has been solved.
Ubuntu 16.04, OpenOffice 4.x & LibreOffice 5.x