Parsing the dates in using date# with only two digit year number is just not fully determined. No idea how QlikView determines the right century, I think that's wild guessing. In my script, it changes the century 1962, so for years <62, it assumes 21 century, then 20th century. Maybe 50 years back in time from now? no idea.
To fix it, I think you need to add the year to your [Date of birth] using string operations, then parse the full four digit year in.
Date(date#(left(DoB,7)&'20'&right(DoB,2),'DD-MMM-YYYY') as DoB,
to use only 2000 to 2099 DoB.
No idea how you should determine the correct century, that's up to you...