He's gorgeous! You're doing such a great job with him.
It's really difficult to tell age in birds but to me Jax looks like an elderly cockatiel. Regarding sex: since Jax is a lutino you can look at the underside of the tail for barring. Mature males won't have tail barring. Jax also has a silver colour to him that I'm not sure of, mutation wise. Are you able to get some more pictures in natural light?