Use as long as you want to. It is YOUR life. There is a HUGE difference between use and abuse. Nothing wrong with a man of ANY age keeping his test levels within the reasonable range for a 20 year old. I think it is bullshit that they lower the levels as we get older. makes no sense. So keep it up but not into the grams use and 4 or 5 compounds and fast burners and diuretics insulin etc. Just run some test maybe 200 - 400 mg a week or less. Donate blood every 8 weeks and have doctor do blood work . Many many people who never used gear never drank smoked or did street drugs will die and or have serious health problems even at a young age. So it is your life enjoy it.
If you abuse your body in any way it causes damage, whether by smoking, suntanning, drinking, poor nutrition, using hormone drugs, etc.
This doesn't make abusing your body smart.
Genetics plays a large role in longevity and health and how resilient your body is to abuse.
You are free in a manner of speaking, depending on legality, to abuse your body and test its limits to such abuse.
Carry on.