It seems that in Internet discussions only women use this interjection.
Is it gender-specific?
It seems that the word "секес"/"секас" is also gender-specific.
What are other gender-specific words in Russian?
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These are not gender-specific words. This is a distortion of normal words used by immature personalities.
Often these distortions are used to mask obscene or indecent words.
I think that "м-да", "м-де", "м-дя" could be translated as "eh", because they express disappointment. It may also be that women often use "мдя" because it sounds similar to the Japanese "nya"...
"Секес", "Секас" refers to sex and the correct spelling is "секс".
To answer your second question, in the Russian language there are no gender-specific words and expressions as far as I can remember.