Applying date range

Hi There

And if anyone can help out you will have saved my day!

To explain I have two sets of merged data. On one fixed column I have two different sets of peoples age

1 - by age grouip eg 25 - 34
2 - By birth year so 01/02/1983

I know that person who is born between 1975 and 1984 would fall into the age group 25 - 34

I want to convert all the birth years into age groups. Its a lot of data (30,000 rows +) in random order

Does anyone have any idea how I would set this up, as I really want to add "age group" to a pivot table I have

Any ideas/suggestions really appreciated

Cheers
Remo