In other words how small can a healthy, normally proportioned person be, and still be considered perfectly normal physically?
Dwarfism is caused by over 200 different conditions. So you really can’t say in an individual case unless they have been ruled out. http://www.clarionledger.com/article/20090402/SPORTS06/904020330/1117
Please define the bolded term.
Seriously, I’m not trying to be snarky. Do you mean within 2 standard deviations of the mean in height? All organs in the correct place? Having 4 limbs and a head?
We had a thread on this about 1-1/2 years ago. This Ask the dwarf (or little person, or almost any other term you want to use) - Miscellaneous and Personal Stuff I Must Share - Straight Dope Message Board tells you a lot about the topic in general. Well worth (re-)reading.
Cutting to the chase, the OP there says in a later post that around 4’10 fully grown is the medical community’s cutoff for “normality”. Shorter than that and you pretty much have to be the result of some developmental failure. The OP herself suggests the cutoff oughta be more like 4’6.
The prominent Italian/Argentinian mathematician Beppo Levi was only 4’6", of normal proportions and healthy enough to live to 86. He moved to Argentina after Mussolini came to power.