Lukosius was born in
Adelaide,
South Australia. His father, Robert, is of
Lithuanian origin and played professional football for
Woodville-West Torrens in the
SANFL. Jack participated in the
Auskick program at Henley and grew up playing high level
Australian rules football and
cricket in Adelaide for Fulham Cricket Club while attending
Henley High School with future Gold Coast teammate
Izak Rankine. Such was his talent in cricket, he was selected as the opening bowler for South Australia at the 2016-17 U17 national carnival but gave the sport away soon after to focus on football. He made his senior
SANFL debut for Woodville-West Torrens in a 2017 preliminary final against
Sturt where he finished with 12 disposals, 8 marks and 4 goals. Leading into his final year of junior football, Lukosius was considered a potential number-one draft pick by many draft analysts and drew comparisons to superstar
St Kilda forward
Nick Riewoldt. In 2018, he played a big part in South Australia's U18 national championships victory and Henley High School's SA schools championship. He also played for Woodville's senior SANFL side but would once again play in a losing preliminary final that year. He was drafted by Gold Coast with their first selection in the
2018 national draft, which was the second pick overall. ==AFL career==