Another complication is that weights and sizes vary by region, and aircraft are configured accordingly if used in a specific region. If I remember correctly the Dutch are the tallest and the Indonesians the shortest. As far as weight is concerned I suppose the Samoans are the heaviest but they probably don't travel much outside their region, and I think the Filipinos the lightest.
Surely pax weights should be recorded at some point as a large group of very heavy (or light) people could slew mass and balance from the average.