Functions cannot change the content or format of a cell
They can return a value
Try this

Public Function AgeIt(mycell)
AgeIt = (Date - mycell.Value) / 365
End Function

In the worksheet call this with, for example, =AGEIT(A1)

See also:
1) David McRitchie's site on "getting started" with VBA
http://www.mvps.org/dmcritchie/excel/getstarted.htm
2) The DATEDIF function
http://www.cpearson.com/excel/datedif.aspx
best wishes
--
Bernard V Liengme
Microsoft Excel MVP
www.stfx.ca/people/bliengme
remove caps from email

"Max" wrote in message
...
Am more familiar with Access, but have created a function in XL07 as
follows:

Public Function AgeIt()
Selection.NumberFormat = "0.00"
ActiveCell.FormulaR1C1 = "=(TODAY()-RC[-1])/365"
AgeIt = ActiveCell.FormulaR1C1
End Function

to calculate a person's age when the birthday is in the cell to the left.

When I select the function and insert it into a cell, I get =AgeIt() on
the
formula bar, but #VALUE! in the cell.

What am I missing???

Thanks in advance for your help.