How tall can a person get through genetics?
Xishun Bao (also known as Xi Shun) is one of the tallest living people at 2.36m tall. Sultan Kösen from Turkey is taller but this is a result of a condition known as "pituitary gigantism", which is the result of an over-production of growth hormone, apparently due to a tumor. So I think 2.36m is about as tall as you can get naturally. Maybe if you could undertake a selective breeding program you could get a bit taller. Goliath was supposed to be either 2.06m (4 cubits and a span) or 2.97m (6 cubits and a span) depending on the source text. My guess is that 2.06m is correct which still would have been pretty impressive for that time.