Gas mask = obvious
trt at an early age = shutting down your natural testosterone over and over again and trying to restart it will have a negative impact on your natural test no matter what age, is this written in stone it all depends on the individual but the cases are high for steroid users to start using trt early than they would of if they didn't do aas.
With every cycle you will most probably produce less and less natural testosterone off cycle, and if you started cycling at a young age ie under 24yrs before your HPTA has fully developed than your up against all this sooner than most IMHO.