If your grandfather's full name was Eric Stanley Plant, according to his World War II record he was born at Stanthorpe 9 Jan 1916.
Queensland BMD records are available to search at https://www.qld.gov.au/law/births-deaths-marriages-and-divorces/family-history-research
According to the Birth Index he was born 9 Jan 1916 in country Queensland, the son of Thomas PLANT & Louisa HUSBANDS. Ref. C3190. He married Nancy SIMS on 21 Dec 1940 in country Queensland, Ref. C5490.
According to the Ryerson Index he died 16 May 2003 age 87, at Sydney, late of Cabramatta.
Thomas PLANT age 36, Louisa PLANT age 38 & Christina PLANT age 2 (all from Derby) sailed as "Nominated Passengers" on the "Roscommon" & arrived at Brisbane on 27 Sep 1912. See Queensland Immigration image
1911 Census entry
FreeBMD has a marriage entry for Thomas PLANT & Louisa HUSBANDS in the December Quarter 1904 in Shardlow registration district; Volume 7b, Page No. 977.
Derbyshire Marriages Transcriptions (© Helen Betteridge & Jean Shannon) on www.findmypast.com: Thomas PLANT, age 29, Bachelor, Butcher, of Ockbrook, son of Thomas PLANT, Butcher & Louisa HUSBANDS, age 30, Spinster, of Foye, Herts, daughter of Charles HUSBANDS, Labourer were married by Banns on 24 Dec 1904 at Ockbrook All Saints, Derbyshire, England. Witnesses were Geo. B. CAMPBELL & Florence PLANT.