Excuse me, but "house inspector" said that? Of the ones I've seen, the
subtelty that escapes them would be "new work" in code requirements.
GFCI might be required in new work next to sink(s), but not required to
be retrofit. Even if it's a good idea.

Assuming your neighbor has a compatible breaker panel, one could put
circuit on GFCI breaker. If not, he could ask "inspector" for
specifics, for 50-yr-old house, and/or tell him to pound sand.

Never mind that most "house inspectors" are most charitably described
as hacks, whose main (only) purpose is to do nothing to offend the
referrer (generally a realtor) for future referrals, and give his payor
some arm-waving. IOW, a joke.

Now, a "building inspector" would be a wholly different critter- a
code-enforcment officer who will pass/fail a real inspection. And
maybe deny a C.O. He/she would not be confused by grandfathered work.

HTH,
John