Rosas Jr was born and raised in Darwin, Northern Territory.
[3] Rosas Jr's grandfather, Bill Dempsey, is a 2022 Australian Football Hall of Fame inductee,[4] an inaugural Hall of Fame inductee in both the WAFL[5] and AFL Northern Territory[6] as well as being named in the Indigenous Team of the Century in 2005.
[7] Rosas Jr grew up playing Australian rules football, rugby league and soccer at high levels but eventually chose to focus on football in his mid-teenage years.
[9] In October 2019, Rosas Jr was drafted to the Gold Coast Suns via their academy pre-selection access.
[10] He made his AFL debut at 19 years of age in round 9, 2021 against the Brisbane Lions in QClash 20 at Metricon Stadium.