There's more than one hormone in the body.
Testosterone is not the only hormone related to growth, and using increased height as a proof of low testosterone is a bit of a throw.
Anyway, I'm arguing with your reasoning -- it's not effective.
randalolson.com/2014/06/23/why-the-dutch-are-so-tall/
Next time, use studies to argue, rather than sillyness:
endocrine.org/news-room/press-release-archives/2006/testosterone_lvls_in_men_decline
but also, do not act as if a single study is proof
here's a tl;dr:
The average levels of the male hormone dropped by 1 percent a year, Dr. Thomas Travison and colleagues from the New England Research Institutes in Watertown, Massachusetts, found. This means that, for example, a 65-year-old man in 2002 would have testosterone levels 15 percent lower than those of a 65-year-old in 1987. This also means that a greater proportion of men in 2002 would have had below-normal testosterone levels than in 1987.
“The entire population is shifting somewhat downward we think,” Travison told Reuters Health. “We’re counting on other studies to confirm this.”
Travison and his team analyzed data from the Massachusetts Male Aging Study, a long-term investigation of aging in about 1,700 Boston-area men. Data from the men were collected for three time intervals: 1987-1989, 1995-1997, and 2002-2004.
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The researchers observed a speedier decline in average testosterone levels than would have been expected with aging alone.
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It’s likely that some sort of environmental exposure is responsible for the testosterone decline, Travison said, although he said attempting to explain what this might be based on the current findings would be “pure conjecture.”
Unfortunately this seems to be the only study on it, so it may be the case that only bostonians are losing testosterone, we'll have to wait and see for later studies.