How do I reference a cell within excel named range?

You can use Excel's Index function:

=INDEX(Age, 5)

"Do you know if there's a way to make this work with relative selections, so that the formula can be "dragged down"/applied across several cells in the same column?"

To make such selection relative simply use ROW formula for a row number in INDEX formula and COLUMN formula for column number in INDEX formula. To make this clearer here is the example:

=INDEX(named_range,ROW(A1),COLUMN(A1))

Assuming the named range starts at A1 this formula simply indexes that range by row and column number of referenced cell and since that reference is relative it changes when you drag the the cell down or to the side, which makes it possible to create whole array of cells easily.