Ha! I think that this suggestion is a myth. To begin with, testosterone is a chemical substance that aids certain functions, so one's physical actions could not necessarily use it up. So, I don't see how masturbating could reduce the production of testosterone. It is like suggesting that testosterone could drive a man to too much sex and then when he has had it, the testosterone would decline and cause low sperm counts. It just doesn't make sense. But then in some societies, adults would tell teenagers such stories to discourage certain behaviours which may have a negative effect on them.

The known effect of masturbating would be losing sensitivity in the genitals because the individuals have become used to arousing themselves that other people could no longer satisfy them no matter how they try.

I hope this answers your question. Thanks a lot for your comment.