Bill, the 1906 Town Register for Paris, Maine (p101) lists Fred H. Decoster as a farmer living in South Paris. Looks like a son Frank E. living in Norway (nextdoor town) with occupation Shoe Shop Operative (there was a shoe manufacturer in Norway) and Deputy Sherriff, and I think Fred's wife Lizzie S.
"Paris, Maine - The Second Hundred Years 1893-1993" shows VRs for 5 DeCostas and 23 Decosters. Among the latter is Frederick H. DeCoster who died January 24, 1934 in Norway, age 82 years, 5 days. Born Greenwood. (I make his birthday January 19, 1852.)
So, not your guy, but maybe a cousin? Worth some time to poke around other Oxford County, Maine town VRs or Genweb forums?