[4] In 2010, prior to the World Junior Championships, Gill threw the 5 kg shot 22.53m at an event in Stockholm, Sweden, exceeding the best-known performances with that weight for 15- and 16-year-olds.

On 11 December 2010, at the New Zealand National Secondary Schools Championships, Gill set a youth (under-18) world-best performance of 23.86m (5 kg).

[8] This performance surpassed the standard for the 2011 Athletics World Championships, however the rules for that competition exclude anyone of Jacko's age competing in any throwing events.

[1][18] On 25 June 2014 in Rarotonga, Gill improved his personal best to 20.70m in winning the shot put title at the 2014 Oceania Area Championships in Athletics.

Jacko was the subject of a "feature" interview for the IAAF's March 2013 monthly on-line newsletter, in which he said he had a keen interest in the shot from an early age: "Since about 10 years old I've decided to write all of my lifting programs and schedules for my training.

In late 2012 he began training under the direction of former New Zealand shot champion Courtney Ireland[2] and was later coached by Kirsten Hellier.