What it means
By tradition, Neptune's sign is a generation's dream: what it idealizes and later gets disappointed in. In Gemini it is a dream of words, knowledge and connection: the belief that explanation and conversation will make the world understandable.
The flip side is confusion in words and facts, believing what you hear without checking. This page is for reference: the next Neptune in Gemini will begin in 2051.
Not about you if you were born after 1902: the next Neptune in Gemini will be for those born in 2051–2066.