when you are on aas your natural test shuts down because you are pumping so much test into your body at once... when you come off cycle you PCT to bring your natural levels back to normal... there is no way of preventing this happening ... you can take hcg to help keep your test flowing while on cycle so that when you come off it's easier on your body...
hope i answered ur question.. dunno if i did or not

Say 2 guys train together and are genetically exactly the same with the exact same level of natural testosterone and the same age etc. One stays natural forever. The other guys does 7 cycles with proper PCT. When they both reach lets say age 31 and the juicer decides to become natural again and never do another cycle, will the guy that did all the cycles have lower natural test levels because of the aas history than the natural guy?

Thats what he is asking.

and once test is replaced synthetically..the body wont produce cause dos't need to...

It's a bunk question because at 31 they should both be on hrt