I noticed they had two different scale pattern into mine has to be see which is not the oldest but still quite exciting!
Yours was minted in 1884. From numista: (1884) 53,702,768 0.56 3.20 9.47 22% 年七十治明 Y#17.2 https://en.numista.com/catalogue/pieces5670.html
Your coin is Meiji year 17 (1884). 明治十七年 (Meiji juunana nen in romaji- or literally "Meiji 17th year").
The Meiji dragon series are some of my favorite coins ever minted. Be careful that you don't become obsessed. The closest coin to the 1 Sen that I have a photo available of is a 1/2 Sen ("半銭") from 1885 or "明治十八年." Pictured below. Japanese read from right to left until the mid-1950s, so you need to read the date, and everything, "backwards" on coins prior to that date. The reverse isn't shown, but it likely has the characters "一銭" or "1 Sen" in the middle and the characters across the top, "以百枚換一圓," mean "100 to a Yen," whereas the 1/2 Sen reads "二百枚換一圓" or "200 to a Yen." This always reminds me of the "1/100" or "1/200" on the reverse of early American cents and half cents. "大日本" or "dai nihon" translates roughly to "Great Japan" or "Empire of Japan" and is how imperial Japan (i.e, prior to WWII) usually referred to itself. Today's Japanese coins use "日本国" or "nihon (or nippon) koku." I'm not sure where you found the 1 Sen, but it was a good find that also provides an introduction to a very fascinating series. For 1884, the 1 Sen had a mintage of 53,702,768 and in the condition pictured is probably worth only a few dollars, but it's still a fascinating thing to come across.
