O'Callaghan joined the Dromtarriffe club at a young age and represented Keale Gaels, an amalgamation of Dromtarriffe and Millstreet, in all grades at juvenile and underage levels. On 18 August2017, O'Callaghan was at left corner-back for the Dromtarriffe junior football team faced St. Kevin's in the final of the Cork Under-21 C Championship. Dromtarriffe secured the title following a 1-14 to 2-08 victory. On 16 September 2018, O'Callaghan was at centre-back when the Dromtarriffe junior hurling team faced Newmarket in the final of the Duhallow Junior Championship. He scored a point from play in the 2-17 to 0-16 victory as Dromtarriffe secured their first ever title in the grade.
O'Callaghan first lined out for Cork as a member of the under-17 team during the 2017 Munster Championship. He made his first appearance at centre-back on 11 April in a 0-16 to 0-06 defeat of Limerick. On 25 April, O'Callaghan captained Cork to the Munster Championship title after a 3-13 to 1-12 defeat of Waterford in the final. He was again at centre-back for Cork's 1-19 to 1-17 All-Ireland final defeat of Dublin at Croke Park on 6 August. As well as being a member of the Cork under-17 team in 2017, O'Callaghan was also selected for the Cork minor team and made his first appearance on 3 May in a 1-24 to 0-08 defeat of Waterford. On 9 July, he was at right corner-back when Cork defeated Clare by 4-21 to 0-16 to win the Munster Championship for the first time since 2008. On 3 September, O'Callaghan was again at right corner-back when Cork suffered a 2-17 to 2-15 All-Ireland final defeat by Galway.
Under-21 and under-20
On 26 August 2018, O'Callaghan was named on the Cork under-21 team as a substitute for the All-Ireland final against Tipperary. He remained on the bench for the 3-13 to 1-16 defeat. On 3 July 2019, O'Callaghan made his first appearance for Cork's inaugural under-20 team in the Munster Championship. He lined out at right corner-back in the 1-20 to 0-16 defeat of Limerick. On 23 July 2019, O'Callaghan again lined out at right corner-back when Cork suffered a 3-15 to 2-17 defeat by Tipperary in the Munster final. He was selected at right corner-back when Cork faced Tipperary for a second time in the All-Ireland final on 24 August 2019, however, he spent much of the game at centre-back. O'Callaghan ended the game on the losing side after a 5-17 to 1-18 defeat.
