Affect calculated variable content to row in table mode

I have integer variable contain the age calculated from birth date entred as a text from birthdate row (i don’t have another method to enter date in table mode view, that’s why i entred it as string). I want to affect this content(age) to the row AGE in the table corresponding to user U. I tried with static text, but it display error and that the roster in Table mode, accept only text and numeric field. I really want to show calculated age in the row.
2) in the same context, how can i show nationality list in the row and select one of them.