What height is tall and what height is considered short depends on the individual’s ethnicity, gender, geographic location, etc. Technically, people would regard a person one standard deviation shorter or taller than the average in their country or group as short or tall, respectively.
The average man in the US is 5’6”. Since statisticians consider 3 inches to be a standard deviation in male height, we can safely say that people would see men below 5’6” as short and men above 5’11 as tall – generally.
However, the technical answer isn’t enough as height perception is subjective. If one is generally shorter or taller than one’s peers in group settings, that’s a more holistic method of determining if they’re short or tall.