This is my Atco edger with a wooden handle. Dating of these is often confusing and difficult. It is understood that they were first introduced in 1923 with wooden handle, and cast plate to hold a spanner. In 1930 a similar version with wooden handle was introduced with detachable grass box or trough  to collect clippings. From 1940's through to 1979's various versions with metal tubular handle. I believe this would place mine in the 1930's category.