Post cycle recovery. How fast your natural T bounces back. Low test for extended periods of time after a cycle leaves your body extremely catabolic. Younger you are the faster you bounce back. More gains you will keep.
IMO, After a cycle you will 'shrink' down eventually if you don't use hormones. Now the rate of this decline can be slowed down by a solid diet and well thought out training regiment. There will be an amount of muscle your body is comfortable holding onto. This dependents on individuals some are at the higher end some average and others not so great.
The 5 year natural training mark is a good indicator of what is attainable by your body without the use of external hormones.
You should refrain from using gear if you haven't weighed the possible future outcome of not recovering and being on TRT for life.