BOL: However, you can change this behavior by changing the setting of CONCAT_NULL_YIELDS_NULL for the current session.
The right answer is: it depends. :-D
Maybe you should specify WHERE in Books Online you found that quote. I am pretty sure that it's on a page that does not describe the CONCAT() function, but other methods of string concatenation. CONCAT() is not affected by this setting.
That being said, it *IS* possible to get this query to error out. If the collation of the database that is active when running this code is different from the default server collation (and hence the collation of tempdb), you will get a collation conflict because the age will be converted to a string in the database collation, and the other arguments are all in the tempdb collation.
Hugo Kornelis, SQL Server/Data Platform MVP (2006-2016)
Visit my SQL Server blog: http://sqlblog.com/blogs/hugo_kornelis