From my observations and through researching, it's less about the damage caused and more about natural hormones at the age of eighteen. The male body (normal) is producing test at peak levels at that age. Not until around the age of 25 do those levels start to drop off, on average. Normally they don't plummet but they do start to take a downhill turn.
Use prior to the age of 25 is, from what I've seen around this board, generally not recommended for that reason. You're still developing at a great rate, why risk shutting all of that down with the use of exogenous hormones?
Not everyone is a pro BB, or will aspire to become one and I think that's the case with the OP. unless those are his aspirations and he sees the rest of his life as him being on stage, there really is no reason to gear up just yet.
Also, at eighteen, most dudes aren't mature enough to cycle properly and don't know how to react if something starts to go wrong. I know when I was eighteen, if I tried cycling, I would have effed it all up.
Just my .02.