I've been trying to come up with some numbers that will impress upon
my son the stark rarity and unique nature of his accomplishment as a
new Private Pilot.


No doubt pilots are few but the small number of pilots isn't such a
big deal. What matters is how many out of those actively seeking pilot
training actually go on to become pilots. That is a far better
indicator of the difficulty involved in becoming a pilot than just the
total number of pilots. The very few private pilots in existence would
be very impressive if everybody in the US had a goal to get a PPL (and
most failed) which is not the case. From what I can tell, those that
show a little bit of inclination to weather the odds do indeed go on
to get their PPLs.