After deating Ifrit I remember talking to Minifillia again and the GC choice begins during that time~ Need a minimum of 20 at least for Ifrit fight during Ph3 so 20 should be accurate ^^ 22 was the capp for Ifrit before so its possible that some people finished at lvl 22 and GC quest unlocked at that time for them later instead of 20 due to lvling up more prolly~