The advent calendar
He is seventeen and does not need one. He is getting one.
Seventeen years old, does not need an advent calendar, does not expect an advent calendar. Getting an advent calendar.
I am not saying what is in it. One clue: everything is flat this year.

What it is
Twenty-four numbered white envelopes. Twenty-four rather than twenty-five, because Christmas here is celebrated on Christmas Eve, standing upright in an old refrigerator storage container.
There is a letter opener in with them, which sounds like a fussy detail and is not. Nobody wants to tear an envelope carefully at seven in the morning.

The numbers
Printed 0 to 9 in a heavy sans face across three sheets of paper.
Taped to a window, reverse side out. That is the whole trick: the window is the lightbox, and working from the back means you trace the mirror image, so when the cut-out is turned over the pencil line is on the underside and does not show.

Trace onto the backs of scraps, whatever is in the drawer: craft paper, leftover gift wrap, offcuts. No two numbers match that way.

Then cut them all out, which took one evening in front of the television, and glue them on with a glue stick.
One to twenty-four.