Date Query

Hi All

Could someone please give me some guidance , I think I have totally lost it.

I am trying to get an age from a dateofbirth field.
1.This is what I have done :

select datepart(year,getdate())- datepart(year,cast(dateofbirth as datetime))
from table

The values are all correct expect everything that has a year of 1949 or below.
This comes thru as 2049 , 2048 , 2047 etc instead of 1949 etc.
I am converting the dateofbirth field to a datetime as this is orginally a character field.

Why would this be happening?

2.If I use this sort of query :

select dateofbirth , datepart(year,getdate())- substring(dateofbirth,1,2)
from table

I get the right age result but in this format - 1948 , 1951, which could then just use the last two digits for the age.

Would there be a simpler way of doing this?

Thanks in advance

Tanya.