1921, yep, but not a Y #35. Your coin has what could be called a snail {that circular winding next to the oval. Y #35 has a different set than either of those.
Look for Y #37 instead, Bob. Krause does note that there may some variation in lettering, but doesn't say more about your 10 Satang.
http://dateconverter.net/thai/?hl=enCredit to Yass for that link.