I feel like 5'6 & below is the cutoff point for being a Manlet. If you are 6'4, that is like a dwarf. So, I get where they are coming from.
I was 5'9 in high school & still am. I think 5'9 is the average height in the United States for males. In the Netherlands 5'9 would probably be a manlet, but they have the tallest people in the world. I have of other desires than being taller.
I think Manlet is more of a state of mind, if a short guy is a cool then't really think of it...if he is overcompensating(ex: Imaginary Lat Syndrome, Lift Shoes, Big Hair) etc than yeah its definitely manlet behaviour.
It seems like Team Alpha Male, iterms is the most Manlet-esque team. It's almost like your not allowed to fight there your over a certain height.