Oh, I make a misunderstanding of the word "mature nature"

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I just see someone judge my old content has mature nature, and when I replay his post, I can't find his post. So I guess this is the alarm content for my post. What do you think I just guess what is the meaning of "mature nature"? I guess it is this kind of post that can popular use for different post, for example, "ok", " I agree with you", "Quite good", something like that. But when I reply one post with the work Pregnant, I am strange I can not post my response, it is alarm with "mature nature" content, I just think it is strange, why, here is not the custom respond, I type it as what I think. After several times' fail, I check the preference, then find I make a misunderstanding for that, it may means it include the content not for young person. Oh, what a big mistake!