Which query performs better when searching a row where a column has maximum?
I'm not sure if this is as platform independent as you think but I've been doing some fairly extensive testing on this in SQL Server recently and the first query was interestingly the fastest.  This was comparing against a number of "tricks" in SQL Server including using CROSS APPLY and windowing functions. But again YMMV in PostgreSQL.

Unless I'm mistaken (I don't know PostgreSQL) your second query will actually come up faster but only because it's going to give you the age for one person.