Giants are exciting, great! I think age largely depends on the gym - for example depending on what age they start kids on team as well as how much they prioritizes uptraining at each level. For example, my daughter's Level 3s group was on the older side at 8-11 yrs old, and giants were not happening there. Giants do not appear to be emphasized at her gym until girls are training to move to Level 7.
My daughter's journey with giants was long. From when she started working on them sporadically in straps and with a spot to when she did them on her own for the first time (12 yr old Level 6) was over a year. She had them briefly but lost them before competition season, during which they were barely training (not in her bar routine). It would almost another year before she got them again and could perform them consistently.