Hey Hamonrye
I started with Altara/Jetstar and can tell you age is NOT an issue. There were a few ladies in our GS over 30 and one guy who was probably 40ish.
I'm not sure about weight. As far as my GS, everyone was pertty healthy, I'm a size 14 which is not too tiny for a girl, but when we tried on our uniforms they had much bigger sizes than that. Good luck!