The average height actually went down since the middle ages, and plummeted to below 170cm in the 17th and 18th centuries, making people like Napoleon which was 168-169CM tall about average for the day.
Being over 6" (182cm) in most caucasian / european descendants nations is considered tall even today.
I'm also not sure what he means by finding "historic armor", modern replicas are made to size, even production runs will have a height range that fits the average modern male (or female, there are replica makers that make armor tailored for women).
Whilst being tall he would also have no much problem finding chain mail or plate to fit a 6" tall person, what he would have is a problem finding one in wearable condition which isn't a museum exhibit ;).
Going further back to say the Roman empire we know based on the documents from the period of Gaius Marius (Marian Reforms) that the required height of a roman legionnaire translated to feet was 5"10-6"0 tall.
http://history.stackexchange.com/questions/17072/average-hei...
" Imperial regulations, though not entirely unambiguous, suggest that the minimum height for new recruits was five Roman feet, seven inches (165 cm., 5'5") ... for the army as a whole a reasonable estimate of a soldier's average height is around 170 cm (5'7").
- Roth, Jonathan, and Jonathan P. Roth. The Logistics of the Roman Army at War: 264 BC-AD 235. Columbia studies in the classical tradition, Vol. 23. Brill, 1999.
"
Page 9 of that same book.
During the later Marian Reforms the height requirements were extended to the rest of the legions including the auxiliaries. That book however doesn't cover that period.
Not sure about minimum heights, but the timeline seems a bit off here...
https://en.wikipedia.org/wiki/Ancient_Roman_units_of_measure...
Roman unit| English name | Equal to | Metric equivalent | Imperial equivalent
pes | (Roman) foot | 1 pes | 296 mm | 0.971 ft
What if the difference is not the average male height, but that extremes are more likely?
Henry the Eighth was 6"1', his field armor is more or less complete and at the met[0], so if anyone has a tall friend in need of a good plate armor you know where to stop ;)