You'll have to explain to us how you calculate 59.
A birthday of either 8 Dec 1950 or 12 Aug 1950 would generally be regarded a
giving an age of 58 as at 13 July 2009. The formula would be
=DATEDIF(A1,TODAY(),"y")
If what you want is what age someone born in 1950 will attain during 2009,
try =YEAR(TODAY())-YEAR(A1)