Sagiquarius, just to try to stay (ahem) on-topic, I just did a quick scan of an ephemeris. Using a 5 degree orb, Neptune and Pluto were in a sextile relationship from roughly 1943 to 1992. Obviously one could narrow this orb, but the sextile actually had a much tighter orb for much of this period. This is why I say it would be a common aspect between two people born at roughly the same year throughout this lengthy period; because both people's Plutos and Neptunes will conjunct one another's at a time when the sextile was in effect. Right now, only seniors older than 67 and young people would not share this aspect with their cohorts.
So in synastry, the Neptune & Pluto sextile on its own would have a generational effect that you would share with your entire age cohort.
Also, to pick up on/debate Ray's point, to get a sextile operating for 40 years, you would have to have plenty of times when Pluto moved faster than Neptune. Otherwise Neptune would have closed the gap, because it generally has a shorter orbit period.
Oren, for anyone born in that 40 year period, the sextile would still pertain. Quite likely, the signs of two people born around the same year would also be the same, unless two people were born around a time when Pluto or Neptune changed signs. So it would make sense to look at house placements, the planets ruling the signs on Neptune's and Pluto's house cusps, and aspects between Neptune or Pluto to personal planets. Beyond that you could look at midpoints, or what-have-you!
And yes, in astrology forums there is a fine line between a member genuinely trying to be helpful in a teaching mode vs. correcting or even goading people as a means of registering her superiority. This line can exist one way in the poster's intention, and in another way in the (annoyed) minds of the recipients of her posts, moreover.