I want to write an expression where I am calculating age(Column B-Column A or Column B-Today() ) by using another column B.
Now I want to select column A and column B for age calculation if any value is selected from Column A and if no value is selected from column A then today's date should be selected.
You might be able to use this (with a slight issue)
Age(Column B, Alt(Column A, Today()))
The issue is that if in case for a particular selection there is only a single value for Column A, then it will pick Column A even if you have not explicitly selected it. In all other scenarios, this should work the same way as tresesco's solution above.
