He was born in South Australia but must have been older than you think
1916 982/497 DRUMMOND Jesse Clement (mother) Myrtle May ALLEN at Angaston
You said he was born to one sister and raised by another sister...here is a birth for a Hazel and Leslie DRUMMOND with mother surname ALLEN.
1913 912/218 DRUMMOND Hazel Iriene (father)George Charles DRUMMOND (mother)Hannah Eliza ALLEN
1919 40A/74 DRUMMOND Leslie Ernest (father)George Charles DRUMMOND (mother) Hannah Eliza ALLEN
Birth of ALLEN sisters
1877 193/472 ALLEN Hannah Eliza (f)Thomas David ALLEN (m)Charlotte BERISFORD
1890 456/79 ALLEN Myrtle May (f)Thomas David ALLEN (m)Charlotte BERRISFORD
You can search yourself at SA BDMhttp://www.genealogysa.org.au/resources/online-databases.htm...